Nuclear magnetic resonance,

Multinuclear H, 13C, 14N, 15N, 170 NMR spectroscopy is widely used for the structural determination of nitroazole derivatives. Some NMR data on the nitroa-zoles have been published in monographs [217-219], thesis [220], and reviews dedicated to five-membered heterocycles [221, 222], the derivatives of pyrazole [223-225], isoxazole [226], oxazole [227,228], thiazole [229], 1,2,4-triazole [230], 1,2,3-triazole [231, 232], indazole [233], and our reports on trimethylsilylazoles [234], NMR of nitroazoles [235], etc. [236-240], 

In the following we will dwell upon the most essential results achieved by the use of NMR spectroscopy in structural and analytical studies of azole nitro derivatives. 

NMR spectroscopy is known to be practically the only convenient method for the investigation of tautomerism, which allows evaluation of the thermodynamical 

The free energy activation of silylotropy in 4-substituted/V-trimethylsilylpyrazoles (4-R-l-TMC-pyrazoles) determined by dynamic NMR method is poorly dependent on the nature of substituent in position 4 [220, 255], Whereas the S29Si in 

AMrimethylsilylpyrazoles is sensitive to the influence of substituent in position 4, the increasing electron-withdrawing properties of those decrease the screening of silicone nucleus (12-22 ppm) [220], 

The only magnetic isotope of germanium is Ge (7.6% abundant) which has I == 9/2, a 

For annual reviews, see Spectrosc. Prop. Inorg. Organometal. Compounds (A Specialist 

McFarlane, W., Nuclear Magnetic Resonance, in George, W. O., Spectroscopic Methods in Organometallic Chemistry, Butterworths, London 1970, pp. 61/94. 

Fedorov, L. A., Nuclear Magnetic Resonance Spectroscopy of Organometallic Allyl Compounds, Usp. Khim. 39 [1970] 1389/423 Russ. Chem. Rev. 39 [1970] 655/72. 

NMR Spectra of the Heavier Elements, in Nachod, F. C., Zuckerman, J. J., Determination of Organic Structures by Physical Methods, Vol. 4, Academic, New York 1971, pp. 233/62. 

Magnetic resonance spectroscopy has a considerable history of being applied to the issue of coal structure. However, as a historical beginning, the structural types in coal were first determined by means of statistical structural analysis (Francis, 1961). One of the first methods to supersede the statistical methods was based on proton (XH) magnetic resonance, which provided a quantitative distribution of the hydrogen types in coal (Brown and Ladner, 1960 Bartle, 1988 Maciel et al., 1993). 

Nuclear magnetic resonance spectroscopy has proved to be of great value in fossil fuel research because it allows rapid and nondestructive determination of the total hydrogen content and distribution of hydrogen among the chemical functional groups present (Bartle and Jones, 1978 Retcofsky and Link, 1978 Petrakis and Edelheit, 1979 Snape et al., 1979 Davidson, 1980, 1986 Miknis, 1982, 1988 Calkins and Spackman, 1986 Cookson and Smith, 1987 Bartle, 

1988 Kershaw, 1989 Botto and Sanada, 1992 Meiler and Meusinger, 1992). However, coal is a structurally diverse material, and caution is to be exercised in the definition of chemical shift expectations. Thus, if structural definition is to be successful, the chemical shift relationships applied to coal and to coal-derived products should be lacking in ambiguity. Sample complexity will usually introduce a variety of ambiguities. 

Like infrared spectroscopy, specific test methods for recording the nuclear magnetic resonance spectroscopy of coal do not exist. It is necessary, therefore, to adapt other methods to the task at hand, provided that the necessary sample preparation protocols and instrumental protocols for recording magnetic resonance spectra are followed to the letter as proposed and described for infrared spectroscopy (Section 9.1). 

Another method (ASTM D-4808) covers the determination of the hydrogen content of petroleum products, including vacuum residua, using a continuous-wave, low-resolution nuclear magnetic resonance spectrometer. Again, sample solubility is a criterion that will not apply to coal but will apply to coal extracts. More recent work has shown that proton magnetic resonance can be applied to solid samples and has opened a new era in coal analysis by this technique (de la Rosa et al., 1993 Jurkiewicz et al 1993). 

Measurements of the nuclear spin-lattice (or longitudinal) relaxation rate Rj are most commonly used to obtain information on the hydrogen jump rates. In favorable cases such measurements allow one to trace the changes in the hydrogen jump rate over the range of four decades. However, the measured values of normally also contain additive contributions not related to hydrogen motion, for example, the contribution due to the hyperfine interaction between nuclear spins and conduction electrons. The motional contribution to the spin-lattice relaxation rate, can be extracted using the difference in the temperature and frequency 

The tracer diffusion coefficient and the jump rate are related by the expression 

Nuclear magnetic resonance (NMR) spectroscopy is a most effective and significant method for observing the structure and dynamics of polymer chains both in solution and in the solid state [1]. Undoubtedly the widest application of NMR spectroscopy is in the field of structure determination. The identification of certain atoms or groups in a molecule as well as their position relative to each other can be obtained by one-, two-, and three-dimensional NMR. Of importance to polymerization of vinyl monomers is the orientation of each vinyl monomer unit to the growing chain tacticity. The time scale involved in NMR measurements makes it possible to study certain rate processes, including chemical reaction rates. Other applications are isomerism, internal relaxation, conformational analysis, and tautomerism. 

Nuclear magnetic resonance (NMR) allows us to detect atomic nuclei and say what sort of environment they are in, within their molecule. Clearly, the hydrogen of, say, propanol s hydroxyl group is 

NMR is incredibly versatile it can even scan living human brains (see picture) but the principle is still the same being able to detect nuclei (and hence atoms) in different environments. We need first to spend some time explaining the principles of NMR. 

When NMR is used medically it is usually called Magnetic Resonance Imaging (MRI) for fear of frightening patients wary of ai things nuclear. 

This picture shows atypical NMR instrument. The extremely powerful superconducting magnet is shown on the left. This model features a robotic arm to change the samples automatically so many spectra can be run overnight. The large box in the centre of the picture is the radio wave generator and receiver. This is much larger than the computer needed to process the data which simply sits on the bench. 

Let us return to the compass for a moment. We have already seen that if we could switch off the earth s magnetic field it would be easy to turn the compass needle round. When it is back on we need to push the needle (do work) to displace it from north. If we turned up the earth s magnetic field still more, it would be e ven harder to displace the compass needle. Exactly how hard it is to turn the compass needle depends on how strong the earth s magnetic field is and also on how well our needle is magnetized—if it is only weakly magnetized, it is much easier to turn it round and, if it isn t magnetized at all, it is free to rotate. 

Nuclear magnetic resonance (NMR) spectroscopy probes the energy required to flip a nuclear spin in the presence of a magnetic field. Computation of this effect 

TABLE 2.6 Comparison of Computed and Experimental Frequencies (cm ) of Glycine  

Given that the chemical shifts for any nucleus can be computed, what are the appropriate methods to employ to obtain accurate values We next describe a number of approaches toward computing chemical shifts and coupling constants, particularly probing for adequate treatments of the quantum mechanics (QM) and basis sets. Additionally, we examine some procedures for using computed NMR spectra to assist in identifying chemical sffucture. (Tantillo has written an excellent review of computation approaches to chemical shifts.) We will end this section with a few case studies where computation played an important role in determining the chemical structure. 

Nuclear magnetic resonance, which is sensitive to short-range order, has been recently used to obtain information on the structure of pores. Two main techniques can be found in the literature [75] one is based on the study of NMR relaxation times of a fluid inside pores and the other on the chemical shift of e trapped in the material. 

The use of the low-field NMR spin-lattice relaxation technique has recently been successfully demonstrated [75-80] as a pore structure tool for porous materials saturated with a solvent (usually water). The basic principle is that the portion of pore fluid near a pore wall undergoes spin-lattice (Tj) and spin-spin (Tj) relaxation in a magnetic field at a faster rate than the bulk fluid. This, coupled with the fast diffusional exchange of fluid between regions within 

Surface affected phase Bulk fluid phase 

From the two-fraction fast-exchange model, the measured Tj can be related to the pore hydraulic radius by 

Another adaptation of the NMR tedmique involves the measurement of the chemical shift of e adsorbed in a sample. The recent development of this last technique has mainly been concerned with the study of the porous structure of microporous materials such as zeolites [81,82], mesoporous silica [11,83], chlat-rates [84], organic polymers and supported metal catalysts [82]. e is an inert 

Nuclear Magnetic Resonance. n.m.r. spectra of 39 thiophen and furan chalcones have been reported, and analysis of the principle components 

Millefiori, G. Scarlata, A. Millefiori, and D. Carbone, Z. Phys. Chem. (Frankfurt am Main), 1981, 128, 63. 

Pinan-Lucarre, J. Loisel, and L. Vincent-Geisse, Chem. Phys., 1981, 62, 251. 

Pinan-Lucarre, D. C. Edewaard, and K. D. Moeller, Spectrochim. Acta, Part A, 1981, 37, 977. 

Proton NMR can distinguish between the different coloured hydrogens. Carbon NMR can distinguish between all the carbons. 

Nuclear Magnetic Resonance (NMR) the Second Moment of the Line shape and Nuclear Spin-Lattice Relaxation 

To compute the lineshape B) and its width AB, one has to sum over the dipole-dipole interactions of aU nuclei with their different distances ty. 

For N nuclei and using a quantum-mechanical treatment, the contribution Hddo( the dipole-dipole interaction to the spin Hamiltonian is 

The factor 1/2 takes into account the fact that the pairs of nuclei should not be doubly counted in the summation, and naturally all summands with i =j are excluded. Each summand leads to a single component of the inhomogeneous NMR hne. In a rigid lattice, the different directions of the r,j are constant in time. The nuclear spins are directionally quantised in the external magnetic field Bq when Bo Bloc- 

For a known crystal structure, each summand in Eq. (5.17) can be computed, and thus in principle the statistical distribution f B) of the resonance field strengths, 

Nuclear Magnetic Resonance. A definitive review of interproton allylic spin-spin coupling has been made which contains much of relevance to alicyclic systems. Study of the n.m.r. spectra of 36 axially and equatorially substituted cyclo-hexanols has identified some unexpected chemical shift effects. Substituent-dependent additive shielding increments were used successfully to calculate the chemical shift of methine H atoms present, so confirming the observation of some axial H atom shifts at lower fields than the equatorial H atom resonances, i.e. an inversion of the accepted behaviour. 

Substituent polarity effects are apparent in the conformational equilibria of cyclohexyl acetate and monochloro- dichloro-, and trichloro-acetates as evidenced by their H n.m.r. spectra. The inversion barriers decrease, and the proportions of axial ester conformer increase, with successive chlorine substitution of the acetate. The conformations of various trans-1,2-disubstituted cyclohexanes have been examined by n.m.r. and a discussion of the observed inversion barriers in terms of steric and dipole-dipole interactions has been given. A new description of these conformational effects is proposed. 

A detailed n.m.r. method is now available for the determination of the absolute configuration of diastereomeric thiol esters. The observed chemical shift data of such esters of hydratropic acid (11) and other phenylacetic acids (12a and b) were found to differ significantly. Since the absolute configuration of hydratropic acid is known the absolute configuration of the thiols can be determined in a relatively simple way from the signs of the differences in signal positions of the constitutionally equivalent protons present. The method is applicable to mixtures of diastereoisomers and hence to the determination of enantiomeric purity. Boat conformations in the t-butylcyclohexanes (13a, b, and c) are caused by 1,3-diaxial interactions of the 

Grenier-Loustalot, A. Lectard, and F. Metras, Org. Magn. Resonance, 1975, 7, 628. 

Nuclear magnetic resonance (NMR) is a powerful technique for investigating the structure of chemical compounds, specially organic matter (Fyfe 1983 SteeUnk et al. 1990 Wilson 1990 Sanders and Hunter 1993). 

Source Swift, R. S., Methods of Soil Analysis. Part 3—Chemical Methods, American Society of Agronomy-Soil Science Society of America, Madison, Wisconsin, 1996. 

Carbon in CH(OH) groups ring C atoms of polysaccharides ether-bonded ali[4iatic C 65-85 

Carbon singly bonded to two O atoms C, anomeric in polysaccharides, acetal or ketal 90-110 

Aromatic C substituted by O and N aromatic ether, phenol, aromatic amines 140-160 

Nuclear magnetic resonance (NMR) line width studies of crystalline polymers are based on the work of Wilson and Pake [102], This method was, however, unsuccessful due to the rather arbitrary decomposition procedures used, which yielded a crystalline fraction that was not in agreement with crystallinity results obtained by the X-ray method. To overcome this difficulty Bergmann [103-105] decomposed the spectrum into three components and this resulted in an excellent agreement between NMR and X-ray crystallinities. Unfortunately, with this method it was not possible to prove the existence of the two amorphous components of the polymer examined. Also, the two amorphous mobilities could not be predicted theoretically. Bergmann [106] succeeded eventually, as discussed next, in improving the separation procedure by finding more suitable line widths for the crystalline and amorphous components of the polymer. In this procedure a new method was evolved for the determination of the crystalline component and of the amorphous component based on a distribution of correlation times, instead of the two discrete correlation times as used in earlier work [103-105], 

Ohta and co-workers [56] studied structural changes leading to creep rupture occurring during creep formation of ultrahigh-strength PE fibres using NMR and WAXD. 

PP = polypropylene PAS, 10 = Nylon 6,10 PETP = polyethylene terephthalate Reprinted from K. Bergmann, Polymer Bulletin, 1981, 5, 355, with permission from  

de Ilarduya and S. Munoz-Guerra, Polymer Degradation and Stability, 2003, 79, 353. 

Canavate, J.J. Sunol, P. Pages, J. Saurina and F. Carrasco, Journal of Applied Polymer Science, 2003, 87, 1685. 

Nuclear magnetic resonance (NMR) is an absorption phenomenon, similar to ultraviolet (UV) and infrared (IR), but the energy of NMR is from radio-frequency radiation by nuclei exposed to a magnetic field. Since Purcell and Bloch in 1946 announced the observation of the phenomenon in bulk matter, NMR has become an indispensable tool in chemistry for the study of molecular stracture and behavior. In this chapter, first we describe the basic theory that underlies the NMR phenomenon. Then we discuss the techniques involved in its spectroscopy. Finally, we illustrate the spectra of some well-known synthetic and biological polymers. We also discuss the advances in this field since 1994. 

Nuclear magnetic resonance spectroscopy of metal 7c-complexes is widely used currently for identification and characterization of metal n-complexes. Both and NMR spectra are commonly reported in contemporary literature. With the increasing availability of instruments capable of studying several different isotopes as well as the enhanced resolution of spectra with the development of commercial 100 and 220 Me instruments, 

NMR spectroscopy seems certain to become even more useful. In addition to its basic function in locating magnetically active nuclei by the measurement of chemical shift and spin-spin coupling parameters, NMR is also extensively applied today to the study of molecular motions and chemical exchange processes. 

In this section a detailed explanation is made of the NMR spectra of some of the more widely studied metal 7c-complex systems. Chemical shifts are reported tau (t) values, this parameter being independent of the oscillator frequency used in the measurement and assuming tetramethylsilane (TMS) as the reference compound with t = 10. Coupling constants (J) are given in cps. 

Nuclear magnetic resonance (NMR) techniques that have been developed for diagnostic analyses of lead in biological matrices and organisms 

Nuclear magnetic resonance (NMR) is a very powerful tool for investigating surfactant systems. The theory of NMR spectroscopy has been described in several books [102-111] and will not be discussed here in detail. The applications of NMR to surfactant systems have been reviewed by Lindman et al. [112]. 

Nuclei do not all have the same resonance frequency because their chemical environment can vary the applied magnetic field. As a result of differences in shielding, nuclei in functional groups have characteristic resonance frequencies. The difference in the resonance frequencies of two chemically and/or magnetically unequal nuclei indicates the chemical shift, expressed in ppm. To calculate the chemical shift, the difference between the resonance frequency of the sample peak and the resonance frequency of the reference peak is divided by the reso- 

Nuclear magnetic resonance spectroscopy yields structural information on surfactants and their micelles, values of the free energy of micellization, AG, and the corresponding enthalpy and entropy changes, and LSh- For the analyses of fluorinated surfactants. H-, C-, and F-NMR spectroscopies have been employed. 

Hao et al. [119] studied sodium perfluorooctanoate (SPFO) and cetyltrimethylammonium bromide (CTAB) mixed solutions by H-NMR. The results indicated a strong interaction between oppositely charged head groups and the penetration of SPFO molecules into the CTAB micelles. Monduzzi et al. [120] identified lyotropic crystalline phases of the ammonium salts of perfluo-ropolyether carboxylic acids by H- and N-NMR spectroscopy. 

For NMR studies of fluorinated surfactants, the most useful nucleus is F, in addition to and H nuclei. Changes ip the F chemical shift at cmc are larger than changes in the proton chemical shifts and, therefore, provide more information on fluorinated surfactants and their micellar structures. F-NMR spectra have been recorded for structural characterization of perfluorononanoic acid [125] and perfluoropolyether surfactants [126]. Micelle formation in solutions of 

The Nuclear magnetic resonance (NMR) image is obtained from the map distribution of spin electrons in a magnetic field and detection of their resonances. The technique can produce detailed information about topography and dynamic movements in either a solution or solid samples. The sensitivity of the technique depends on the amount of magnetic field introduced into the sample and the sample state itself, such as its temperature. NMR technique is limited to the sample size, which has to fit within the magnetic coils (ranges up to 30 cm in diameter) [81]. 

The property of a nucleus that allows magnetic interactions, i.e. the property possessed by and but not by is spin, if you conceive of a and nucleus spinning, you can see how the nucleus can point in one direction—it is the axis of the spin that is aligned with or against the field. 

Likewise, for a nucleus in a magnetic field, the difference in energy between the nuclear spin aligned with and against the applied field depends on  

A H or nucleus in a magnetic field can have two energy levels, and energy is needed to flip 

The sample of the unknown compound is dissolved in a suitable solvent, placed in a narrow tube, and put inside a very strong electromagnet. To even out imperfections in 

Nuclear spin is quantized and has the symbol I. The exact number of different energy levels a nudeus can adopt is detemiined by the value of /of the particular isotope.The nuclear spin /can have various values such as 0, V2, 1, 2- the number of energy levels is given by 21+ 1. Some examples are H, J= V2 (= 

The transition energy can also be described as a frequency of electromagnetic radiation  

In the nuclear (e.g. proton) part of a molecule, the external field is changed by factors which are characteristic for that molecule. The resonance frequency of isolated protons is shifted in a way typical of the chemical compound in which the proton is located. This shift is called the chemical shift of the resonance frequency (at a given external magnetic field). 

The chemical shifts are small, e.g. at a proton up to 30 ppm of the used frequency, if 100 MHz (108 Hz) is used 10 ppm corresponds to 103 Hz. The shift is normally not measured absolutely, but compared with the known frequency of a reference substance, e.g. for protons tetramethylsilane (TMS). The area of the resonance is proportional to the number of nuclei which give rise to it. 

In aqueous solutions with small molecules the relaxation is slow (0.1-0.5 s), while tgSR of ice is very small (some 10 3 s) [1.36]. Close to the glass temperature of a substance the relaxation time does not decrease exponentially and thus a different means of description must be used [3.9]. 

Harz et al. [1.39] demonstrated by NMR spectroscopy that freezing of food (e.g. grapefruit juice) almost never followed the ideal expectation. The crystallization of carbohydrates is much hindered and further reduced by the high viscosity of the so- 

The advantage of nuclear magnetic resonance (NMR) lies in the fact that measurements occur in aqueous solutions, i.e. the most natural form if one considers biological materials. NMR is widely used for structural characterizations of carbohydrates even though the requirements for homogeneous probes and relative insensitivity can pose limitations. The flexibility of carbohydrates sets another factor of limitation and therefore structural and dynamic properties must be determined in a combination of different methods [112]. Conformations of bound carbohydrates 

Choppin, Gregory R. Liljenzin, Jan-Olov and Rydberg, Jan (2001). Radiochemistry ard Nuclear Chemistry, 3rd edition. Woburn, MA Butterworth-Heinemann. 

Friedlander, Gerhart Kennedy, Joseph W. Macias, Edward S. and Miller, Julian (1981). Nuclear and Radiochemistry, 3rd edition. New York Wiley-Interscience. 

FusEdWeb Fusion Energy Educational Web Site. Available from http //fusedweb. pppl.gov . 

Nuclear magnetic resonance (NMR) is one of the most useful analytical methods in modern chemistry. It is used to determine the structure of new natural and synthetic compounds, the purity of compounds, and the course of a chemical reaction as well as the association of compotmds in solution that might lead to chemical reactions. Although many different kinds of nuclei will produce a spectrum, hydrogen (H) nuclei historically have been the ones most studied. NMR spectroscopy is particularly useful in the study of organic molecules because these usually incorporate a large number of hydrogen atoms. 

Spectroscopic Methods.—Nuclear Magnetic Resonance (n.m.r.). Cohen-Addad and Ruby comment that thermodynamic polymer-solvent interaction parameters obtained from n.m.r. data should be contrasted with those obtained from other methods in the sense that the former are defined on a molecular scale only. That is, nuclear spins are local probes, sensitive to magnetic interactions averaged over volumes of molecular size. N.m.r. methods, therefore, usefully complement other methods in studying underlying statistical mechanical models for polymer-solvent mixtures at equilibrium a comment which has been amplified in relation to polymer blends.  

Dipolar spin decoupling has been used to study the numbers of contacts of various types and the free energy of formation of a single mixed contact. Sp6vacek et al. used temperature dependence of chemical shifts in H-n.m.r. spectra to examine the specific interactions in poly(methyl methacrylate) solutions. Cabane has used n.m.r. methods to study aggregation in aqueous polymer detergent systems. Compatibility and phase structure in polymer mix- 

A unique feature of NMR that applies to the phenomena of interest here is that the proximity to a diamagnetic solid of a paramagnetic surface alters the relaxation times of the nuclei in the latter. Thus, by following this magnitude with respect to reference data for pure phases, it is possible to probe the proximity of a given 

To each of the discrete orientations assumed by the nuclear magnetic moment vector in the external magnetic field corresponds an energy of interaction E (Fig. 1)  

If the transition is to result from the absorption of electromagnetic radiation, the frequency, v, of this radiation must be such that the transition energy for one nucleus can be expressed as the energy of one absorbed quantum, i.e. 

We now want to show that the frequency of radiation necessary for a transition between nuclear energy levels is equal to the Larmor frequency, Uo (defined in equation 7). 

The vast majority of NMR experiments (viz., all Fourier transform NMR techniques) are performed using short pulses of radiation. It is clear that by varying the duration of the pulse, tp, and the field intensity Hi contained in the pulse of radiation, one can rotate M in the zy plane by any desired angle i/( to the z axis according to  

the quantum mechanical and classical mechanical treatments of nuclear magnetic resonance closely correspond, as has been demonstrated mathematically [ ]  

A ID NMR experiment provides information on the chemical shift and spin-spin coupling fine structure of the individual resonances in the spectrum. Double or multiple pulse irradiation experiments provide additional data on through bond scalar connectivities or through space dipolar connectivities, which relate to resonance assignments, conformational state and dynamics of the molecules under investigation. 

The pulse methods rely on selective irradiation of a particular resonance line with a radio frequency (rf) and observation of the resulting effects in the rest of the spectrum. Among commonly employed methods are 2D correlated spectroscopy (COSY), 2D spin-echo correlated spectroscopy (SECSY), 2D nuclear Overhauser and exchange spectroscopy (NOESY), 2D J-resolved spectroscopy (2D-J), and relayed coherence-transfer spectroscopy (RELAYED-COSY) (Wutrich, 1986). 

In two-dimensional techniques, prior to the observation pulse with the detection period t2, an rf pulse is applied with the evolution period y between the two pulses. A second time dimension (COSY) is created by repeating the same experiment with the incrementation of H. For each value of ti a free induction decay (FID) is recorded and, after 2D Fourier transformation, the desired 2D frequency spectrum S(wi,w2) is obtained. In the NOESY spectroscopy, the mixing period consisting of two 90° pulses separated by the mixing time Tm is used. The general experimental scheme for 

In combination, the 2D NMR spectroscopy allows the determination of resonance frequency (w,), chemical shift (6), relaxation times (T] and T2) for each NMR active atoms, coupling constant (J) between adjacent atoms, and parameters of Overhauser enhancement experiments (NOE). These data make a basis for establishing chemical structure and measurement of dynamics of the molecules under investigation. The main trends in recent NMR research on protein and enzymes involve the development and employment of the following methods 1) NMR spectroscopy with maximal high 

According to the theory ofLipardi and Szabo (1982), values of the spin-lattice (1/Tj) and spin-spin (1/T2) relaxation rates are dependent on three important structural and dynamic parameters. The first parameter d is proportional to pjp/r3, where p and pj are magnetic moments of nuclei interacting through space, and r is the distance between the nuclei. The second parameter c is proportional to the anisotropy of the nuclear chemical shift. In the spin-lattice relaxation case, the third parameter is the spectral density function  

These results have been obtained using ID NMR techniques. The recent improvement of 2D-NMR techniques as applied to paramagnetic molecules is likely to yield additional structural information in the near future [196]. Recent experiments on horseradish peroxidase have shown that 2D techniques are possible, despite fast proton relaxation rates due to the presence of high-spin iron [197], 

Whatever the derivative considered, the nuclear magnetic resonance spectra of thiazoles are remarkably simple and apparently univoque. The first proton NMR spectrum of thiazole was described by Bak et al. (171). It was followed by a series of works establishing a systematic description 

TABLE L3L PROTON CHEMICAL SHIFTS OF THIA20LE AND VARIOUS MONOSUBSrrrUTED THIAZOLES  

Making allowance for those effects gives a good correlation between the chemical shifts and the it- and/or tr-electron density of the carbon atom bearing the proton (133, 236,237). 

More elaborated calculations based on theoretical LCAO models have given interesting results within the CNDO/1 and CNDO/2 approximations (251.) Tables 1-32 and 1-33). 

KJtoS KJ(OKJS KJ10KJKJKJKJ10N tON KJKJKJN KJKJK KJtON KJN KIN N -- N3N N3N N3S N l N N  

We considered electron spin resonance spectroscopy before nuclear magnetic resonance spectroscopy because ESR deals primarily with the subatomic particles most popular in our treatment of quantum mechanics the electrons. However, atoms also have nuclei, which have many of the same properties that electrons have. In particular, many nuclei also have a total spin and a magnetic dipole. 

Unless otherwise noted, all art on this page is Cengage Learning 2014. 

Compare the relative magnitudes of the electron s magnetic moment and the proton s magnetic moment. Why are they different  

The magnetic moment of the hydrogen atom nucleus, a proton, is 2.443 X 10 J/T. The electronic magnetic moment is found by using equation 16.10  

Because certain nuclei have a magnetic dipole, they experience a potential energy when they are subjected to a magnetic field. As with electrons, there are 27-1-1 different possible orientations of the nuclear spin when subjected to a magnetic field, and each orientation has its own change in total energy A ,ag. In the presence of a 

Two dipoles ju and e situated at a distance interact with an energy proportional to (//,. // )/r,2. The dipolar interactions have the effect of broadening the resonance frequencies. The magnitude of this 

Nuclei Natural abundance % Larmour frequency MHz (at 10 Gauss) Magnetic moment (in nuclear magnetons) Spin (in h units) Electric quadrupole moment (10 cm ) 

Of greater interest to the chemistry of glasses is the chemical shift interaction term. This arises from the fact that the extra nuclear electrons in the atom also respond to the applied magnetic field by virtue of which they shield the nucleus from the external magnetic field. As a consequence, a small shift occurs in the resonance frequency and this is known as the chemical shift. It is measured in parts per million (ppm). The chemical shift interaction energy, Ecs can be written as. 

Where a is the chemical shift tensor. The observed resonance frequency V is given by. 

Another important interaction which contributes to broadening of resonance peaks is the quadurpolar interaction. When the nuclear spin, / 1, the nuclei possess electric quadurpole moment, eQ. The quadurpole moment 0 is a measure of the distortion of spherical symmetry of the nuclear charge distribution. Quadurpole moment interacts with the electric field gradient, EFG, present at the nucleus. These are the fields caused by the electrons in the atom. Spherical distribution of electrons in closed shells do not produce any EFG at the nucleus but the bonding electrons do. Therefore the quadurpolar interaction can be used to obtain information on chemical bonding. Quadurpolar interaction shifts the Zeeman levels. The first order correction due to quadurpolar interaction to the Zeeman splitting between levels m and (w-1) is given by. 

The NMR technique utilizes the macroscopic magnetic moment resulting from the nuclei in the sample. In an external magnetic field B the nuclear spin I can have 21+1 different orientations. The energy of a magnetic sublevel is given by 

Modern NMR spectroscopy frequently uses pulsed RF radiation and the observation is performed instead in the time domain. Pulsed NMR can be utilized in different ways. If a short pulse of high field strength (-lO T) and duration tp is applied, the magnetic moments will be rotated by an angle a around 

NMR techniques are used for studying the chemical composition as well as the detailed structure and bond character of molecules. Kinetic processes, such as rotations and inversions of molecules, can also be studied. NMR has found many industrial applications, especially in measurements on foodstuffs. The strength of the proton signal yields the concentration of a hydrogen-containing substance. The signal of protons in a solid matrix decays faster than that for a liquid sample. This property can be used for fast measurements of moisture content or oil assessment in seeds, etc. NMR spectroscopy has been discussed in [7.41-43]. 

In order to appreciate its application to kinetics, a brief outline of the nuclear magnetic resonance phenomenon will be given. This treatment will be rather pic- 

Two protons will precess at the same angular velocity only when the magnetic field strengths at their nuclei are the same. In any situation of chemical interest they are bonded to other species, and the applied magnetic field is shielded to some extent by the bonding electrons and further modified by the other charged parts of the molecule. In a molecule containing two or more non-equivalent protons, the NMR peaks do not come at the same place and the difference between the two positions or their positions relative to a standard—the chemical shift 5— is of in- 

I In practice, it is easier to keep to fixed and to vary the steady magnetic field Ho- This has the effect of varying the precession frequency Wo- 

Ideally, then, the most kinetic information may be obtained from an nmr signal by comparing the observed with the computed pattern. In many cases this is not possible, or at best very tedious, yet very good approximations of the relevant rate constants may be obtained in a much more straightforward way. 

Suppose there are two protons, in environments A and B, in the system under investigation, and that they have resonances at frequencies 0 and cOo, respectively, with no spin coupling between them the kinetics of possible exchange between A and B are to be followed. Suppose also that the concentrations of A and B are equal (although this is not an important restriction since the treatment has been extended to the more general case where Cg). The observed spectrum comprises two lines of equal intensity separated by 8 = (Da —cogl, the chemical shift. The term t is now introduced, and this represents the mean lifetime of states A and B, or the time spent by the proton in the environments A and B. (If the concentrations o 

1 he last two decades have seen a dramatic increase in the applications of nuclear magnetic resonance techniques m colloid and surface science. The reasons for this are two-fold first, the availability of economical high-field superconducting magnets and, secondly, the development of fast and compact digital computers. These advances have made it possible not only to expand the range of available nuclei that can be observed but also to improve the sensitivity of the method. 

The technique of NMR imaging, now finding important applications in diagnostic medicine, can also be used in other ways, enabling for example the distribution of oil in rocks or of macroscopic phase transitions in alloys to be detected and studied. 

NMR methods can also be used for structural analysis, detecting the local geometries around specific cations in zeolites and so complementing the information obtained by zY-ray diffraction. 

In the analysis of pure organic compounds, virtually all hydrogen and carbon atoms can be identified by using high resolution and nuclear magnetic 

NMR is a versatile spectroscopic technique for studying opaque heterogeneous samples, which has already been proven to have a number of useful applications in dairy research (Duce et al., 1995). The technique is also suitable for at-line and on/in-line process control. NMR is based on the magnetic properties of the nucleus of certain atoms, such as the nucleus of the hydrogen atom, lH, the nucleus of carbon-13, 13C, and the nucleus of phosphorus-31, 31P. It is convenient to divide the parameters obtained from NMR spectra into static and dynamic parameters. 

The presence of magnetic moments /lia, b, of nuclei A,B. in a molecule are responsible for the two observables of the NMR experiment that are most frequently utilized in chemical applications. They are physically observed in form of quantized energy differences AE that can be measured very precisely. These two observables are the nuclear shielding tensor cr for nucleus A and the so-called indirect reduced coupling tensor KAB for a pair of nuclei A,B. Both crA and Kab are second-rank tensors that are defined via the phenomenological Hamiltonians 

The speed with which NMR spectroscopy has been incorporated into scientific inquiry is truly amazing. The first commercial spectrometers became available in the 1950s. By the middle 1980s whole bodies could be placed in the probes of NMR spectrometers (magnetic resonance imaging) and the structures of body parts could be determined in exquisite detail. Today structures of proteins and other macromolecules in solution or in the solid state are determined routinely. What was unthinkable in the 1960s is routinely practiced today even by undergraduates The power of the method and the structural detail it provides have no doubt fueled its rapid development. 

Fortunately for organic chemists, hydrogen and carbon are the most common nuclei found in organic compounds, and the ability to probe these nuclei by NMR is invaluable for organic structure determination. Since proton magnetic resonance (PMR) is tire most common type, tire behavior of nuclei in magnetic fields will serve as a model for other nuclei which have spin quantum numbers I = and thus behave similarly (13C, 19F, etc.). 

Still another type of spectroscopy was added to the chemist s bag of tricks in 1946. In principle, it is similar to electron spin resonance, but it, is based on the spins of atomic nuclei, rather than electron spin. Nuclear spin resonance (or, as it is more often called, nuclear magnetic resonance) developed phenomenally in the 1950 s, and today it is a versatile source of structural information. 

Suppose now that the energy difference between spin levels is evaluated for a particular nucleus in number of different compounds. It is found that this difference is very slightly (but, with good resolution, unmistakably) dependent on molecular environment. With the frequency of exciting radiation held constant, the protons in H2 absorb energy at a slightly different field strength than those in H20, and these, in turn, 

Similarly, NMR studies of dihorane, B Hfi (p. 129) show two different types of protons (corresponding to the terminal and bridge hydrogens) in a 2 1 ratio. 

A most interesting application of nuclear spin resonance spectroscopy is the study of very fast reactions, particularly the transfer of hydrogen ions from one species to another. In the acid base equilibrium 

Recently it has been found that the NMR spectrum of trimethyl-aluminum dimer, VI, shows the two expected proton peaks (corresponding to the bridge methyls and terminal methyls ) at —75° C, 

Although evaluations of harmonic force constants [d E dq,dqj), elearic polarizabilities d EIdeide ), and dipole moment derivatives (d E/d ,dqj) are perhaps the most common applications of second-order properties (or, equivalently, second derivatives), other areas of interest to chemists can be treated with these techniques. One such field of application that holds great promise for the future is the calculation of nuclear magnetic resonance chemical shifts. 

Elements of the chemical shift tensor ct for a particular nucleus t) are given by the mixed second derivative of the energy with respect to the nuclear magnetic moments [/,/n)] and the magnetic field [B,] 

Applications of the GIAO approach at the SCF level are now relatively routine, but correlated calculations are more difficult because the most convenient implementations of this approach require the analytic evaluation of the second derivatives. Therefore, correlated studies using GIAO basis functions are effectively limited to levels of theory for which analytic second-derivative methods are available. Although the number of calculations thus far carried out on chemical shifts is far too small to give us a clear picture of basis set and correlation effeas, the initial results of GIAO-MBPT(2) calculations suggest that correlation is indeed important for these phenomena. In Table 31 are results from a few representative calculations of chemical shifts. 

From these results and a limited number of other studies, it appears that the correlation effects are most pronounced for systems with multiple bonds, which should come as no surprise. In addition, it appears that basis set and correlation effects tend to aa in different directions, which, of course, can lead 

Noniterative T3 contributions can be added to QCISD just as in the CCSD case. The contribution from double excitations to T3 is formally exactly the same T(CCSD) term, except that it is evaluated using QCISD coefficients, that is, T(QCISD). QCISD(T) further adds a single excitation term like CCSD(T), but it needs to be multiplied by 2 compared to CCSD because the C3 term remaining in Eq. [89] introduces this term once and iteratively in CCSD. 

Vibrational spectroscopy is a molecule-specific analytical method that probes the vibrations of molecules and solids. Fourier transform infrared (FTIR) and Raman spectroscopies are widely used in situ techniques in the analysis of chemical reactions. However, in the case of silicalite-1 synthesis, they have not yet been used [35]. Attenuated total reflectance infrared (ATR-IR) spectroscopy has however been used to study soluble silicates and shown to be able to characterize various structures [25, 35-37]. It is likely only a matter of time before we see ATR-IR used under in situ conditions. 

This technique continues to be that preferred by organic chemists to study tautomerism. Some reviews relevant for tautomerism have appeared  

133) High-Resolution Solid-State NMR Study of Reversible 1,5-Proton Shifts in Organic Solids [90MRC(S)29] NMR of Pyrazoles  

The quantity 7 is different for different nuclei and in particular for different isotopes of the same element. 

A magnetic dipole moment, when placed in an external magnetic field, will have an energy of interaction E with the field which is the negative of the product of the magnetic field H and the component of the magnetic moment along the field direction fin 

An energy level scheme is shown in Fig. 1 for a nucleus with I = such as the proton (7 = 2.675 X 10 gauss second ) where 2 X + 1 =2 energy levels occur. Equation (4) is the fundamental spectroscopic relationship of NMR. 

As one may verify by direct quantum mechanical calculation (S), the application of an oscillating magnetic field. Hi, of angular frequency , will cause transitions of the nuclear spin between adjacent magnetic energy 

at thermal equilibrium there will be a net absorption of energy from the electromagnetic field. As can be seen from the value of 7 given above for the proton, the frequency required for resonance in a magnetic field of several kilogauss is in the radiofrequency range and of the order of 10 c.p.s. 

Since atoms in different environments experience different chemical shifts, measuring the chemical shift can give information about the local environments of the atoms. The measurements can be interpreted empirically but in many 

In this equation A and M are fitted constants that are the same for all ions having the same electron core. Skibsted et al. (1996,1998) have used this method for calculating the quadrupole coupling constants of Cs and 

AE in eq. (1.7) and Fig. 1.3(b) is the difference between the energies of precession along and opposite to B0. Using eq. (1.7), the Larmor precession frequency v0 of nuclei with / = 4 can be calculated, recalling that AE also equals h v0  

For a field strength of 2.13 Tesla, the Larmor frequency of, 3C is in the order of 22 to 23 MHz, much lower than that of H (90 MHz). This is in the radio-frequency (rf) range. 

An alternating magnetic field Bl with frequency irradiating an ensemble of nuclear spins precessing in the static field B0 may overcome the energy difference AE if it meets two conditions The vector of the alternating field B1 must rotate in the plane of precession with the Larmor frequency v0 of the nuclei to be observed (Fig. 1.4(a)). 

As a result, the spins originally precessing with B0 flip over, and now precess against B(). Absorption of energy AE from B, takes place (nuclear magnetic resonance). 

In order to observe NMR, a sample containing nuclear spins (e.g. H, 13C) is placed in a static magnetic field B0. An alternating field B with radio frequency v, is applied perpendicularly to BQ. Usually, v, is increased or decreased slowly and continuously 

13C-NMR is the most informative technique for the elucidation of chemical structures, but generally requires large sample sizes as a result of the low abundance of 13C. As a consequence, micro-sampling to obtain tissue specific information is practically impossible. In addition, the amount of time required for the acquisition of NMR spectra makes this technique unsuitable for the analysis of large samples. 

Advanced NMR techniques have resulted in the elucidation of novel lignin structures, involving, for example, the benzodioxan structure involving [3-0-4 and a-O-5 linkages between two monolignol residues (1.89 Ralph et al., 2001 Marita et al., 2003). In addition, NMR has been used to determine the impact of mutations and introduction of transgenic constructs on lignin subunit composition (Ralph et al., 1997 Marita et al., 1999 Marita et al., 2003). 

While structures in the solid state do not necessarily parallel those in solution, they have been used to explain solution-phase behavior where other evidence is not available. For example, the conformation of the isopropyl groups in the highly substituted pyridine 16 in the solid state is as shown, as a result of the substituents adjacent on the ring 2004JOC536 . This was used to account for the greatly reduced nucleophilicity of this species. 

The application of NMR spectroscopy to structure determination is broad however, in this section the group of studies that allow fundamental properties of the pyridine moiety, particularly electronic distribution, will be discussed. Application to other aspects, such as conformation and tautomerism, is discussed separately in those sections below. 

NMR spectroscopy has been useful in determining the extent of charge transfer in species such as the pyrido-neimines and pyridonemethides. This demonstrates that the predominant canonical form of pyridoneimine is the aromatic zwitterion 19, while the major canonical form for pyridonemethide is the quinoid 20 2001JOC8883 . In a similar vein, 13C NMR spectra have been used to study polarization of the ethylene bond in pyridine chalcone derivatives such as 21 as a result of conjugation with the pyridine moiety 1999JST(482)371 . 

Along with solution-state NMR spectroscopy, analysis of the solid-state spectra of nitrogen heterocycles has been carried out to evaluate the various chemical shift tensors associated with the 1SN nucleus 1997JA9804 . Importantly, this showed the dominance of the tensor perpendicular to the plane of the aromatic system along with the key effect of protonation of the pyridine nitrogen. 

Similar studies support the NMR spectral evidence detailed above, supporting the predominance of the zwitter-ionic form of the merocyanines 22 and 23 1997JA10192 though different shifts in absorbance maxima were observed due to the ability of the /-butyl substituents to shield the adjacent oxygen atom. 

The quantity I characterizes the scalar magnitude of the spin angular momentum vector, which is given by 

Nuclei with a nonzero nuclear spin quantum number also have a magnetic moment. The magnitude 

Additionally, the scalar magnitude of the magnetic dipole moment vector is given by [43] 

On the other hand, the z-component quantum number is then denoted by mx, where 

Owing to the fact that the proton mass is higher than the electron mass, the nuclear magnetic moments are about 2000 times smaller than the electron spin magnetic moments. 

Since the nucleus is spinning, this torque causes Pn to process (in the way a spinning top processes under the torque of a gravitational field) about B (Z) at an angular frequency where 

Quantum mechanics requires that the magnetic moment vector (g. ) component in the direction of the field is restricted to values  

The frequency of the radiation corresponding to this energy (and that would be absorbed in bringing about the transition) would be  

A simplified illustration of the apparatus used in NMR measurements is shown in Fig. 2.41. The magnet applies an external field, commonly of L5 T (15 kG, although fields up to 50 kG are now used), the strength of 

The resonance frequency measured in NMR is normally expressed in terms of units independent of the spectrometer field strength and hence as a chemical shift (8) in parts per million with respect to a reference compound [i.e.,8 = (// ampic - f/rcfere,.ceVv,(10 ), where and are positions of the respective absorption lines (in Hz) and v is the spectrometer operating frequency]. 

Sawa et al. have compared the framework Al determined by Al NMR with the acid amount determined by NH3 TPD for a series of mordenite zeolites. They found 

Rgure 8 Si MAS-NMR spectrum of LZY-62 zeolite with Si/Al = 2JS. Band assignment is given in text. 

Hie value of Si/Al ratio can be converted to Al content and thus, as in Al NMR, to a value for Brpnsted acid sites density. 

The use of Si NMR is limited to zeolites with sufficiently high lattice Al to give a range of environments for the Si atoms. In general, this method is applicable to zeolites with Si/Al ratios lower than 15. 

Marcelin and coworkers have shown that both Al and Si NMR techniques correlate well with other methods in terms of determining total number of Br0nsted sites in zeolites.  

Specific problems concerning inorganic materials, where NMR has been applied, include the structure of amorphous materials, melts, and the detection of small amounts of phases in mixtures. 

The nuclides of most interest are protons ( H) and carbon-13 ( C) for organic molecules, though others such as phosphorous and silicon can be used. NMR spectroscopy is most useful as a qualitative tool for determining the structure and identity of molecules. It is rich in information content but can be poor in sensitivity. Most NMR instruments today are based on FT-NMR. 

Radiofrequency (RF) transmitters generate frequencies of a few MHz to almost 1 GHz, which irradiate the sample molecules. If the energy difference between the relevant spin states is matched by the RF pulse, the nuclei will move to the higher spin state and be in resonance with the magnetic field. In older instruments, either the frequency sweep 

When the resonant condition is met, the NMR signal is collected at the RF receivers. NMR signals are generally weak and need to be amplified and processed prior to further analysis. Using the pulsed mode, the free induction decay (FID) spectrum in the time domain is recorded and while it contains all the information on frequencies, splitting and integrals, it must be converted into the frequency domain by Fourier Transformation (FT). This FT step enhances the S/N ratio of the signal. 

At the computer, the huge amount of information is processed and spectral searching and matching can be carried out. NMR spectra can be very complex, especially two-dimensional (2-D) experiments, and may require detailed data analysis and interpretation. Libraries can be very useful for assigning structure and identifying compounds. 

New cryoprobes are coming on stream that are designed for multipurpose NMR measurements of four different nuclei - phosphorus, carbon, nitrogen and hydrogen. There is no need to change probe between the different experiments. 

In a-Si H NMR techniques have been useful primarily for the determination of local structural arrangements. Studies of H NMR at elevated temperatures, or at lower temperatures after annealing at elevated temperatures, have probed the details of hydrogen evolution in a-Si H. In undoped films both hydrogen (in the form of H and D) and silicon ( Si) have been investigated. In doped films studies have been reported for boron ( B), phosphorus ( P), and fluorine ( F). A second useful result of the H NMR measurements in a-Si H has been the inferred existence of trapped H2 molecules from spin-lattice relaxation measurements. The presence of these molecules has been very difficult to observe by other experimental techniques. 

Measurements that employ NMR often provide a very detailed, albeit very local, probe of structural arrangements and bonding. The important terms in the Hamiltonian for most situations of interest in NMR in a-Si H are given by 

(1) the first term is the nuclear Zeeman interaction, which is of the form 

The second term in Eq. (1) is the dipolar interaction between nuclear spins, which can be written as 

The third term in Eq. (1) is the so-called chemical shift interaction, which results from a complicated interplay between the electronic Zeeman contribution to Hand the interaction between electronic and nuclear spins. In an applied field, the electronic Zeeman contribution polarizes the electronic spins, which can then interact via both their orbitd and spin components with the nuclear spins. These interactions in general produce both amag-netic and paramagnetic contributions to the local magnetic field experienced by a nucleus in a solid. Because all of the electrons are in principle involved in this interaction, the situation is complicated to the point where one usually writes in parameterized form as 

Chemical novelty is not as important a criterion for inclusion in a primary fragment library because unique composition of matter desirable for patent protection is expected to be added later during the sprouting and merging HTL chemistry phase. There are several vendors of fragment libraries who accumulate fragments from various sources and then cluster, package and resell them. 

Use of primaiy data sprouting and merging to create secondary libraries 

As previously stated, NMR is the technique most represented in the literature as being used to detect a fragment binding event, for both historical and technical reasons. 

The STD-NMR experiment is carried out such that ligand saturation, effected when the ligand is bound to the protein, is actually measured on the free ligand, not the bound-state ligand. This is achieved by requiring that the 

STD-NMR was used to screen a set of 34 potential binders to the SI pocket of human Factor Xa. Fragments 9-12 were observed to produce the strongest STD signals. 

The mechanical and dielectric loss methods are based on the different mobilities of the chain segment or dipoles bound to them in the solid state and in the melt. These differences lead to an anomalous dispersion of the modulus of elasticity (see Section 11.4.4) or the relative permittivity (see Section 13.1.2) and to corresponding losses in the mechanical or the electrical alternating fields. 

Part of the work performed on a sample will be converted irreversibly into random thermal motion by movement of the molecules or molecule segments. This loss passes through a maximum at the appropriate transition temperature or relaxation frequency in the associated alternating mechanical field (torsion pendulum test). A similar effect is obtained by the delayed response of the dipoles with dielectric measurements. Therefore, dielectric measurements can be made only on polar polymers. According to the 

The NMR data tabulated below were all measured on solutions of alkali metal salts MPHg in various liquid solvents, specifically NH3 [1 to 4] and dimethylformamide (DMF) [5 to 7]. However, it is not known, whether MPHg in these solutions is completely ionized into M + PH rather one has to assume an equilibrium between PHi (doubly connected P) and MPHg (triply connected P), see a compilation of ip NMR data [8]. Solutions were obtained not only by direct dissolution of MPHg, but also by reacting PH3 with NaNHg suspended in liquid NH3. This latter method may suffer from the additional difficulty of proton exchange between PH2 and PH3, see [1, 2]. 

The shifts 6( H) and 6(3ip) and spin-spin coupling constants J(3ip,iH) were derived from the H NMR doublets (splitting by ip with 1=1/2) and the ip NMR triplets (splitting by two protons), which were observed in the experimental systems described above, and are listed in the table below regardless of the difficulties in assigning the spectra. 6( H) is referred to TMS and is positive for low-field shifts see a compilation of chemical shifts of protons directly bonded to P [10]. is referred to 85% H3PO4 (also positive for low-field shifts) see a review on ip NMR spectra [11]. For details and supplemental information, see the remarks below the table  

The anisotropies of J(3ip,iH) and J(iH,iH) have been theoretically investigated assuming several geometries of the PH ion [14]. 

A 3ip nuclear shielding a = 663.5 ppm and an anisotropy Aa=306.2 ppm were obtained by an ab initio calculation in the gauge including atomic orbital (GIAO) method for an optimized geometry [15]. An experimental value of a = 607.8 ppm was based [15] on the shift measured in [4] and on the absolute shielding scale (a = 328.4 ppm for POl ) given in [16]. 

The diamagnetic shielding at P and H was calculated by an ab initio MO-SCF method for the calculated equilibrium geometry [17]. 

Nuclei of certain isotopes (e.g. possess intrinsic angular 

Carbon forms the backbone of all organic molecules, and Carbon-13 ( C) is the only magnetic carbon isotope (Wehrli, Marchand and Wehrli, 1988). From the point of view of the organic chemist, it is fortunate that such an isotope exists, forming some 1.1% by weight of naturally occurring carbon (Stryer, 1981). 

In the field of olive oils, NMR has been applied before (Anon., 1994 Bianchi et al, 1993, 1994a Gussoni et al., 1993 IFR, 1994 Zamora, Navarro and Hidalgo, 1994), demonstrating the potential of this technique for analysing olive oils. Brekke et al. (1990) and Kvalheim et al. (1985) also show that a combination of NMR and PCA can be used to distinguish between different North Sea crude oils. 

Theory. The magnitude of the spin (angular momentum) of the nucleus is h[I I +1)], where I is the nuclear spin quantum number and ft is the reduced Planck s constant h/ln. I may have only integral or half-integral values (0, 1, 1 ). 6, in units of h/ln) (Friebolin, 1993), the value being 

In a nucleus containing an even number of both protons and neutrons, 7 = 0. This includes the common atoms and This leads to considerable simplification of the spectra of organic molecules. The reason for this is that nucleons with opposite spin can pair (though neutrons can pair only with neutrons, and protons with protons), just as electrons pair. If the numbers of neutrons and/or protons is odd, then the spin is non-zero, though the actual value depends upon orbital-type internucleon interactions (Akitt, 1983). 

Infrared spectroscopy has been used to characterize the structures of silica-filled polydimethylsiloxane (PDMS).  

Other optical and spectroscopic techniques are also important, including positron annihilation lifetime spectroscopy, spectroscopic ellip-sometry, confocal Raman spectroscopy, and photoluminescence spectroscopy. Surface-enhanced Raman spectroscopy has been made tunable using gold nanorods and strain control on elastomeric PDMS substrates.  

Both transmission electron microscopy and AFM have been used to characterize the structures of silica-filled PDMS. Another example of an application to polysiloxane elastomers is the characterization of binodal and spinodal phase-separated structures occurring in model PDMS networks.  

Although NMR has been used to characterize some aspects of polymerization (e.g., copolymerization kinetics), the applications most 

Most elastomers require reinforcing fillers to function effectively, and NMR has been used to characterize the structure of such composites as well. One examples is the adsorption of chains onto filler surfaces, -and the strong absorption of these chains into bound rubber —for example, PDMS immobilized onto high surface area silica. - Another example is the use of NMR to image the filler or polymer itself. ° NMR has also been used to study the phase separation and order of water molecules and silanol groups in polysiloxane networks and the activation of transport and local dynamics in polysiloxane-based salt-in-polymer electrolytes.  

Values of the chemical shift 6 and the spin coupling constant J( N- F) are compiled below 6 is defined positive in the high field direction, RT=room temperature. 

Value refers to the isolated molecule and was obtained by extrapolation of gas phase values to zero density by means of virial coefficients for a, see below. 

A study of F NMR spectra of gaseous samples at different densities q and temperatures T served to obtain the virial coefficients of the shielding constant a, defined by the power series expansion a(T,Q) = ao(T) + ai(T)-Q + a2(T)-g2H—. The densities were kept sufficiently low so 

The principal components o, v = a, 3, y, of the chemical shift tensor were determined from NMR spectra of NF3 trapped in 3-quinol clathrates at temperatures around 4.2 K (NF3 molecules become oriented under these conditions). Values in ppm are a =-60 30, Op = 260 40, o = -200 30. The a axis is in the plane of the fluorine triangle, and the 3 axis is along an N-F bond. The chemical shift tensor is defined as traceless, i.e., the mean chemical shift o = V32a = 0 [10]. 

The width of the F NMR line in solid NF3 has been measured as a function of temperature from 4.2 K up to the triple point at 66.37 K. These measurements, together with the temperature dependence of nuclear quadrupole resonance frequencies, were analyzed in terms of hindered rotations [11], see also p. 201. 

The influence of the hydroxy-group on the chemical shifts of simple cyclo-hexanols has been examined, and the stereochemical dependence of the shift 

Ungaretti, and A. Corsico Piccolini, Cryst. Structure Comm., 1975, 4, 683.. 

An extensive study of the conformational equilibria of a series of nine 4,4-disub-stituted-l,l-dimethoxycyclohexanes (9) using n.m.r. spectroscopy has cast doubt on the usual substituent additivity principle. The free-energy difference of the two chair forms at 200 K was determined. It was found that in the 4-methyl-4-vinyl and 4-methyl-4-phenyl compounds the conformer with the methyl group equatorial is favoured by 836 and 1423 J mol respectively. An axial methyl conformation is preferred for the corresponding methyl-benzyl, methyl-chloromethyl, methyl-dichloromethyl, and methyl-cyclohexyl compounds, by 1046, 1339, 1673, and 1255 Jmol . The difference for the methyl-trichlorbmethyl and phenyl-isopropyl compounds exceeds 5 kJ mol with both methyl and phenyl axial 

evidence obtained at 250 MHz has been used to show that the trans-triaxial-2,3,6-tribromo-4-methylcyclohexanone (lOa) undergoes a spontaneous dyo-tropic rearrangement in the solid state to give the trans-diequatorial isomer (10b). From the n.m.r. parameters it was concluded that the triaxial isomer is somewhat deformed by syn-diaxial interactions of the bromine atoms. 

Carbon-13 n.m.r. spectra of numerous thiazoles, 1,2,3-thiadiazoles, and benzothiazoles have been reported and correlated with the electronic effects of substituents. Replacement of one or more of the phenyl groups in the cyclo- 

Mossbauer spectra have been reported for some tellurium heterocycles e.g., (8). The complete structure of 1,2,5-thiadiazole (9) has been determined by double-resonance modulation (DRM) microwave spectroscopy.  

General.—Recent publications include a chapter on thiophens in a comprehensive treatise an article on recent advances in the synthesis of benzo[6]thiophens a published plenary lecture on condensed thiophens, especially thienothiophens, selenolothiophens, and related systems and a review on the synthesis of polycyclic thiophens from the direct insertion of heterosulphur bridges into vinylarenes, biaryls, and angularly condensed arenes,  

NMR is an important experimental tool for polymer science and is used to study molecular structure and dynamics. The technique is a key method in the design of new polymers and can be used to identify atoms present, functional groups, and their configurations. NMR is also useful for measuring the average molar mass of a material, molecular tumbling correlation times, and other localized dynamics. 

The NMR technique was first discovered in the 1940s and takes advantage of the behavior of nuclear spins in a material when subjected to an applied magnetic field. All nuclei have a property called spin associated with them. In a simplistic model, you could think of the atomic nucleus as a rotating body with some angular momentum. This angular momentum is quantized and therefore can only take certain values these values are 

The nucleus is analogous to a tiny bar magnet and so has an associated magnetic moment p. When placed in an external magnetic field H, the nuclear spins tend to line up either parallel to the field direction or in the opposite direction (antiparallel). These two spin states have different associated energies separated by 

A key feature of NMR spectroscopy is that the magnetic field to which a nucleus is exposed is not just equal to the applied field but is modified by the chemical environment of the nucleus. This results in a spectrum of 

The resonant frequency for a particular nucleus (say H) depends on the applied magnetic field for the instrument so these frequencies must be expressed as shifts from a reference material, a compound added to the sample with a clear, sharp NMR signal is used, typically tetramethylsilane (TMS). The position of the NMR signal relative to the reference sample for a particular nucleus is known as the chemical shift. 

Solid state NMR offers the ability to observe molecular homogeneity from the molecular levels to over 20 nm. Proton NMR or CPMAS NMR studies can measure the proton spin-lattice 

Chemical shifts in the C-NMR spectra can provide evidence of specific interaction between dissimilar components of the blend. A method termed cross-polarization, magic angle spinning (CPMAS- CNMR) has shown promise in identification of the environment of carbon nuclei in blends along with an assessment of the degree of homogeneity. Xe-NMR has been employed to determine structural order in amorphous blends. Xenon as a probe molecule will show separate resonances for a phase separated blend, but singular values for miscible blends. Examples where NMR techniques have been utilized for polymer blends will be briefly noted in this section. Reviews on the use of solid-state NMR to study the miscibility and characteristics of polymer blends include [223,224]. 

Flgure5.26 2D NOE spectrum of a 40% (w/w) equal weight mixture of PS/PVME at 65 °C (0.1s mixing time).The intrachain PS and PVME connectivities are in the upper part and the interchain in the lower part of the spectrum (reproduced (replotted) with permission from reference Mirau, P. A.,Tanaka, H.and Bovey, E A.,Macromolecules (1988) 21, p. 2929, copyright (1988) American Chemical Society) 

Flgure5.27 CP/MAS NMR spectra of phenoxy/poly(4-vinyl pyridine) biends showing evidence of 

PEO PMMA HNMR Tgdata showed miscibility NMR data showed PEO motion impaired by PMMA but not frozen in 254 

Bach [7]. Its Cm versus T behavior near Tc was fitted on exponential laws in various ways and compared with data for Eui ySrySeo.5So.5, see Westerholt et al. [10] and Westerholt, Sobotta [11 ]. 

Application of magnetic field at 2 K transforms antiferromagnetic EuSe0.95S0.05 at low internal fields (-0.9 kOe) into the ferrimagnetic state and at 1.5 kOe into the ferromagnetic state (cf. p. 206) [7]. EuSeo.sSo.i, presumably at 2.2 K, under a hydrostatic pressure of 4 kbar is said to be ferromagnetic, Schwob [12]. 

This approach is widely used for the determination of the diffusion coefficients of the various components in microemulsions, namely the oil, water and surfactant(s). These measurements are useful in elucidating the structural changes occurring in microemulsions with changes in composition or environmental conditions. It is also helpful in establishing the presence of long-range order and particle anisotropy (Moulik and Paid, 1998). 

Microemulsions have been attracting considerable attention due to properties such as ease of formation, thermodynamic stability, transparency and high solubilization capacity. Microemulsions are excellent delivery systems for nutraceuticals (Rozner et al., 2007,2008) and as vehicles for chemical reactions, such as acid autocatalysis (Mcllwaine et al, 2008). They have also been used for the separation and purification of proteins, metal extraction and as drug delivery systems (Hatton, 1989 Pileni, 1989 Garti et al, 2006 Spemath and Aserin, 2006 Kogan et al, 2007). 

Four examples of the type of structural information that can be obtained from NMR experiments are as follows. 

Determination of valence state and local environment The chemical shift differs for the same atom in different valence states and local environments. In addition, the coupling of the nuclear spin with neighboring nuclei gives a different fine structure for different environments. This method may be particularly useful for the identification of the many molecular-like clusters in amorphous materials. 

In a rigid structure, dipole-dipole interactions introduce variations in local fields that broaden the resonance lines. Line narrowing with increasing temperature may signal the onset of additional vibrational or rotational degrees of freedom. In crystalline NH4CI, the proton linewidth widens at temperatures below 135 K where the proton positions become ordered. 

Interatomic distances can sometimes be determined from NMR linewidths. Proton-proton distances in gypsum (CaS04 2H2O) and other hydrates have been measured to an accuracy of 0.02 A. 

The quadrupole interaction energy is zero if the nuclear spin / I, or if the nucleus is in a high-symmetry field such that V = 0. 

---

J A measure of the coupling constant in nuclear magnetic resonance. 

One has seen that the number of individual components in a hydrocarbon cut increases rapidly with its boiling point. It is thereby out of the question to resolve such a cut to its individual components instead of the analysis by family given by mass spectrometry, one may prefer a distribution by type of carbon. This can be done by infrared absorption spectrometry which also has other applications in the petroleum industry. Another distribution is possible which describes a cut in tei ns of a set of structural patterns using nuclear magnetic resonance of hydrogen (or carbon) this can thus describe the average molecule in the fraction under study. 

Starting from these methods, as we will see further on, nuclear magnetic resonance (NMR) of carbon has provided an absolute percentage of aromatic, paraffinic, and naphthenic carbons. 

Determining the Parameters of a Petroleum Fraction by Nuclear Magnetic Resonance... 

Schematic view showing the principle of nuclear magnetic resonance.

Brown, J.K. and W.R. Ladner Jr (1960), Distribution in coallike materials by high-resolution nuclear magnetic resonance spectroscopy . Fuel, Vol. 39, p. 87. 

NMR Nuclear magnetic resonance [223, 224] Chemical shift of splitting of nuclear spin states in a magnetic field H [225], C [226, 227], N [228], F [229], 2 Xe [230] Other Techniques Chemical state diffusion of adsorbed species... 

Ernst R R, Bodenhausen G and Wokaun A 1987 Principles of Nuclear Magnetic Resonance in One and Two Dimensions (Oxford Clarendon)... 

Lynden-Bell R M and Harris R K 1969 Nuclear Magnetic Resonance Spectroscopy (London Nelson) pp 81-3... 

Venanzi T J 1982 Nuclear magnetic resonance coupling constants and electronic structure in molecules J. Chem. Educ. 59 144-8... 

Morris G A and Freeman R 1979 Enhancement of nuclear magnetic resonance signals by polarization transfer J. Am. Chem. See. 101 760-2... 

Bax A 1982 2-Dimensional Nuclear Magnetic Resonance in Liquids (Delft Delft University Press)... 

Figure Bl.13.6. The basic elements of a NOESY spectrum. (Reproduced by penuission of Wiley from Williamson M P 1996 Encyclopedia of Nuclear Magnetic Resonance ed D M Grant and R K Harris (Chichester Wiley) pp 3262-71).

Bloembergen N, Purcell E M and Pound R V 1948 Relaxation effects In nuclear magnetic resonance absorption Phys. Rev. 73 679-712... 

Lipari G and Szabo A 1982 Model-free approach to the interpretation of nuclear magnetic resonance relaxation in macromolecules 1. Theory and range of validity J. Am. Chem. Soc. 104 4546-59... 

Carr H Y and Purcell E M 1954 Effects of diffusion on free precession in nuclear magnetic resonance experiments Rhys. Rev. 94 630-8... 

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