Nuclear-Magnetic-Resonance Spectra

The nmr spectra of bridgehead substituted adamantanes are generally readily analyzed since, for the most part, only minor spin-spin coupling is observed in these substrates. The chemical shifts induced by various bridgehead substituents are found to be remarkably additive 150T Knowing the chemical shifts pro- 

The chemical shifts of 1-substituted adamantanes are correlated well with substituent electronegativity 15°) as measured by a 152 or group dipole moments 153X Only the chemical shifts observed for the 7 (bridgehead) position exhibit the normal inductive order, however the chemical shifts of the 0 (adjacent methylene) and 5 (far methylene) hydrogens appear to be anisotropy controlled 150 . 

Solvent effects upon the chemical shifts of 1-substituted adamantanes are also highly specific 15°). Aromatic solvents, especially benzene, give rise to significant solvent shifts of all resonances to a higher field. The / hydrogens, which are closest to the substituent, are affected least, however. The manner in which these geometrically specific effects are produced is not clear. No evidence for the existence of thermodynamic 1 1 complexes is found. Apparently, specific solvent ordering results from an interaction of the solvent with the dipole moment of the solute 1S4). 

The nmr spectrum of 1-chloroadamantane in SbFs-S02 s°) or of adaman-tane in SbFs-FS03H 157) is attributed to the 1-adamantyl cation. The essential characteristics of the spectrum are summarized in Table 4. Contrary to the normal observation where the hydrogens adjacent to the carbonium ion site experience the largest deshielding effect, the 7 (bridgehead) hydrogens of the 

1-adamantyl cation appear furthest downfield. This anomalous chemical shift is also observed in the spectrum of the 1-diamantyl cation (58) obtained from the SbF5-FS03H solution of diamantane 1S7 . 

Nitrogen-15 n.m.r. spectra of alkanesulphonamides, benzenesulphonamides, and isothiocyanates have been reported. Nitrogen-14 n.q.r. data on methane-sulphonamide and AW-disubstituted analogues have established a valuable application of the technique, i.e. to assess the degree of delocalization of the lone 

Selenium-7 7 n.m.r. data for selenols, selenides, selenomum salts, diselenides, and selenoxy-acids have been obtained under conditions (i.e. on the same spectrometer) which allow reliable comparisons of spectral parameters to be made. Benzeneseleninic acids ° and selenolesters have also been studied by this technique, and Se spin-lattice relaxation times of organoselenium compounds have been collected in a pioneering study 

Tellurium-125 n.m.r. spectra of telluroesters have been determined,  

557 [MeSH, MejS, MejSj, MejS, and EtSSMe] J. 

Nuclear magnetic resonance is an invaluable tool for investigating dihy-droazines and, in particular, the dihydropyridazines. Unfortunately, until recently, most investigators have reported only proton resonance data. No doubt, in the future, more attention will be paid to 13C and 15N, which can contribute much information. 

The most useful applications of NMR have been in structural determinations and in identifying the presence of tautomeric equilibria. 

The nuclear magnetic resonance (NMR) spectrum may provide information on the types of fundamental groups present in a molecule and the stereochemical relationships between neighbouring groups. The resonance of H, C, and nuclei in a magnetic field have all found considerable use in phosphorus chemistry, and this has been aided considerably by the advent of Fourier transform techniques [65,73,79,84]. 

The NMR spectra of P compounds were reported by Dickinson as long ago as 1951 [78] and since that time the role of this technique in P chemistry has steadily grown. Work carried out in the subsequent 15 years was comprehensively reviewed in 1967 by Van Wazer and others [65]. 

The stable isotope of phosphorus, P, has a spin of /= 1/2, and the natural resonance frequency for this nucleus is much lower than that for H. Although a given nucleus has one characteristic resonance frequency for a specified external field strength, this frequency will, in practice, be modified by shielding effects arising from chemical bonding which influence the actual field strength at the nucleus. 

The frequency modifications, known as chemical shifts are usually measured with respect to the single sharp absorption in 85% orthophosphoric acid, which is used as an external standard. The same nucleus, if in a similar chemical environment, either within the same molecule, or in different kinds of molecules, will in general show the same kind of chemical shift. The chemical shift is given by the expression 

The relative intensities of resonance are proportional to the relative numbers of nuclei producing them. Comparatively large samples are, however, needed to study P resonance because of the rather low sensitivity of the element to magnetic fields (Table 14.9). The relative sensitivity for equal numbers of atomic nuclei at constant field strength is 

Nuclear Magnetic Resonance Spectra.—Natural-abundance S n.m.r. of representative sulphur compounds appears to offer little scope for structural identification purposes the broad absorption peaks render chemical-shift measurement very inaccurate. Some H- Se and H- Te doubleresonance studies reveal a similar structure-dependence of Se and Te chemical shifts, comparable with that of P.  

Conformational information derived from n.m.r. and i.r. studies of 2,4-di-nitrophenyl 2-chloroalkyl sulphides ArSCHR CHClR reveals a weak repulsive interaction between Cl and SAr, while an intramolecular attractive 

Kajimoto, M. Kobayashi, and T. Fueno, Bull. Chem. Soc. Japan, 1973, 46, 1422. 

Hayami, N. Tanaka, N. Hihara, and A. Kaji, Tetrahedron Letters, 1973, 385. 

Protonation equilibria for aliphatic sulphoxides in H2SO4, as determined by n.m.r., compare well with data obtained earlier by u.v. and c.d. methods. pKbh Values obtained similarly for sulphinates and sulphides have been reported values for sulphides are some 4 units more positive than for corresponding ethers, and a basicity order RjS RSSR RSH emerges, in interesting contrast with the oxygen series (MeOH is more basic than MeOMe). C N.nLr. of DMSO and diethyl sulphoxide reveal O-protonation in strong acid since both CH, and CHz resonances are shifted to higher field.-  

For Se-based chalcogenide glasses, due to the low NMR sensitivity of selenium, it is very time consuming to record NMR spectra (more than three days for one spectrum). Nevertheless, Bureau et al. measured Se NMR spectra of As Sej.x and Ge Sci. glasses at ambient temperature [80] and found that three lines appeared in the arsenic-selenium spectra that could be assigned to Se-Se-Se at 850 ppm, As-Se-Se at 550 ppm, and As-Se-As at 380 ppm, as shown in Fig. 4.9. In contrast, only two lines appeared for Ge Sci. glasses that were assigned to Se-Se-Se at 850 ppm and Ge-Se-Ge at 430 ppm, respectively, as also shown in Fig. 4.9. 

Gjersing et al. employed magic-angle-spinning (MAS) NMR to investigate the structure of Ge fSe, with 5 x 33.3 where crystalline (3-GeSe2 was used as a reference. The NMR spectra were decomposed into four different chemical surroundings, as shown in 

NMR spectra of GeSe and AsSe glasses (reproduced from Ref. 80). Reprinted from ]. Non-Cryst. Solids S26 327, Bureau B., Troles Floch M. L., Smektala R, and Lucas J., Medium range order studies in selenide glasses by 77Se NMR, 58-63, Copyright (2003), with permission from Elsevier. 

The proton NMR spectrum of 1,10-phenanthroline has been obtained and analyzed by several authors in nonaqueous solvents and in water at various pH values. Examples of studies of the NMR spectra of substituted 1,10-phenanthrolines that have been investigated in some detail are also worthy of mention. The NMR spectra of all ten phenanthrolines have been determined in deuterochloroform, and the spectra were interpreted (Table IV). The spectra of the 1,7-, 1,10-, and 4,7-isomers have also been compared with that of phenanthrene. Shifts in the NMR spectrum of 1,10-phenanthroline induced by a europium shift reagent have been discussed, and C chemical shifts of free and protonated 1,10-phenanthroline were measured.  

The mass spectra of all the parent phenanthrolines have been reported. As expected, the spectra are dominated by the peak due to the molecular ion, and there is relatively little fragmentation. The mass spectra of some oxidation products of 1,10-phenanthroline have also been briefly described. 5a 

Norden, R. Hakansson, and M. Sundbom, Acta Chem. Scand. 26,429 (1972). T. Hoshi, H. Inoue, J. Yoshino, T. Masamoto, and Y. Tanizaki, Z. Phys. Chem. Franitfuri) 81, 23 (1972). 

Martin, N. Defay, F. Geerts-Evrard, and D. Bogaert-Verhoogen, Tetrahedron Suppl. 8, Part 1, 181 (1966). 

Norden, R. Hakansson, and M. Sundbom, Acta Chem. Scand. 26,429 (1972). 

Ohtsuru, K. Tori, and H. Watanabe, Chem. Pharm. Bull Tokyo) 15, 1015 (1967). 

Since both fluorine and phosphorus have nuclear spin / = in 100% natural abundance, nuclear magnetic resonance studies have not surprisingly occupied an important place in the development of the chemistry of tervalent phosphorus fluorides. 

Analysis of the NMR spectra also leads to the evaluation of the phosphorus-phosphorus coupling constant and provides evidence concerning the relative signs of the directly bonded Vpp and the remote (Vpp or Vpp,) phosphorus-fluorine coupling constants (see Table IX). 

A preliminary report 223) describes the temperature dependence of Vpp in F2PSPF2. There is a steady increase in Vpp from 302 Hz at —1°C to 393 Hz at —120°C and this has been attributed to either P-S-P bond angle changes in excited vibrational states of the molecule or to internal rotation about the P-S bond. EtN(PF2)2 also shows a tempera- 

The NMR spectrum of the recently synthesized 1,3-ditertiary-butyl-2,4-difluorodiazadiphosphetidine (which is an XAA X spin system X = fluorine, A = phosphorus) has been analysed and the trans-annular phosphorus-phosphorus coupling constant found to be 92.5 Hz 260a). 

Tetelbaum et al. (315) have suggested that a correlation exists between Sp for compounds of the type XPF2 (where the group X is alkyl, aryl, or halogenoalkyl) and the Taft a parameter for X. While it is true that the lowest-fleld chemical shifts (—200 to —250 ppm) occur for the alkyl derivatives, values for other fluorophosphines sometimes show irregular variations (Tables II-VI) even within fairly closely related compounds. 

Nuclear magnetic resonance (NMR) spectroscopy is at present one of the most widely applied physical techniques in biology, and its potential applications increase day by day, as more sophisticated instrumentation becomes available and deeper theoretical knowledge is obtained. The phenomenon of NMR was discovered simultaneously by Purcell and his associates at Harvard University and by Bloch and co-workers at Stanford University, for which they were jointly awarded the Nobel prize in physics in 1952. In the lipid field there are two main types of NMR spectroscopy that are of interest broad-line experiments, concerned mainly with the spectra obtained from samples in the solid state, or from oriented phases, and narrow-line, or high-resolution, experiments carried out with samples in the liquid, solution or gas phases. Both types of NMR spectroscopy are extremely useful in the study of the lipids. In addition, Fourier transform (FT) NMR has helped increase the sensitivity of the technique and the so-called pulse method of recording spectra has literally widened the prospect of NMR applications in the field of lipid research and industry. The application of NMR to solid fats is still in its infancy (Pines et aL, 1973 Schaefer and Stejskal, 1979 BocieketaL, 1985). 

The energy of interaction of the nuclear dipole and the static field is given by the scalar product of vectors // and H  

The minus sign means that the alignment with the lowest energy is with the magnetic moment parallel to the field direction, which is known as the z direction. 

The energy E is quantized. Quantum-mechanical calculations constrain the values of the z component of jjL that lies along the field to 

The ratio of nuclei in the alignments depends on the Boltzmann factor where k is Boltzmann s 

Carbon-13 NMR (13C-NMR) signals of aryl carbon atoms bonded directly to boron can be broad and/or low-intensity peaks. In some cases, they may not be observed, possibly depending on the quadrupolar relaxation rate of boron nuclei (79MI1) (Fig. 1). Some special techniques are known to increase the intensity of 13C signals of these carbon atoms (77JOM(132)29 78JOMC34). 

Resonance interaction between the boron atom and the five-membered heteroaromatic ring accounts for the downfield shift of the ring carbons, particulaly the strong deshielding of the C-3 and C-5 carbon atoms (79JOM15) (Fig. 2). 

Tabulated l3C chemical shift data for pyridylboranes show that deshielding of ring carbons is less signficant in comparison with those of five-membered heteroarylboranes, but the C-3 carbon in 3-pyridylborane is conspicuously deshielded (31 ppm) (83CPB4573 87UP1) (Fig. 3). 

Lower field shifts of H signals at the 3- and 5-positions in 2-borylated five-membered heteroaromatics have been observed (76CB1075), suggesting that the ir-interaction to boron is also significant (Table I). 

Proton NMR data for pyridylboranes are given (83CPB4573 87UP1) in Fig. 4 those of heteroarylboronic acids are available in the literature (70CR(C)1608 71MI1 76BSF(2)1999 77CS76). 

Similarly, a linear plot is obtained when the 13C chemical shifts of the bridgehead carbon atoms are compared with the C-C(bridgehead)-C angle for four triptycenes (22). Thus by calculating CPC and C-C(bridgehead)-C angles in a variety of as yet unknown triptycenes, Hellwinkel (22) has been able to predict their 31P and 13C (bridgehead) chemical shifts. 

A detailed, simultaneous analysis (35) of the proton-decoupled 13C NMR spectrum and of the 13C satellites in the proton-decoupled 31P spectrum has allowed all the 31P-31P and 13C -31P coupling constants in 1,6-diphosphatriptycene to be evaluated (Table III). The large C(2)-P(l) coupling and small C(l)-P(6) coupling are considered to be strongly dependent on the orientation of the phosphorus lone-pair electrons and 

The AA component in the 19F spectrum of (MeSi)2(C6F4)3 presumably has the shape shown in Fig. 9 due to additional H-F coupling as would be expected from this, complex splitting of the methyl resonance is observed in the proton spectrum. The 19F NMR spectrum of P2(C6F4)3 exhibits a symmetrical doublet in the AA component due to phosphorus-fluorine coupling, each half of the doublet being identical to the XX component Jnp-i F = 60.2 Hz. 

Symmetrical M2(C6F4)3 triptycenes show three 13C resonances for the Cj, C2, and C3 types of carbon atom, the chemical shift of Cj being 

3 Chemical shifts are in ppm from external capillary TMS. Coupling constants are in Hzs. 

In Order to prove that stable alkyl cations, and not exchanging donoracceptor complexes were obtained, we also investigated the l3C nuclear magnetic resonance of the potentially electropositive carbenium carbon atom in alkyl cations31-32  

The 13+C shift in the r-butyl cation (CH3)313+C 1 in S02ClF-SbF5 solution at —20 ° is at S13c 335.2 (all CMR shifts are from 13C TMS) with a long-range coupling to the methyl protons of 3.6 Hertz. 

Substitution of the methyl group in the r-butyl cation by hydrogen thus causes an upfield shift of 10.4 ppm. Although the CMR shift of the carbocation center of the r-butyl cation is more deshielded than that of the isopropyl cation (by about 10 ppm), this can be explained by the methyl substituent effect, which may amount to 22 ppm. The tertiary butyl cation thus is more delocalized and stable than the secondary isopropyl. 

The 13C+ shift in the r-amyl cation C2H5C+(CH3)2 3 is at 613C 335.4 which is similar to that of r-butyl cation. The shift difference is much smaller than the 17 ppm found in the case of the related alkanes, although the shift observed is in the same direction. The 13C NMR chemical shifts and coupling constants Jc-h of C3-C8 alkyl cations 1—13 are shown in Tables 2 and 332.  

Considerable interest is attached to the spectrum of the bridge protons, which is actually a septet with the theoretical intensity ratio 1 2 3 4 3 2 1, the latter being a reflection of the statistical weights of the possible combined spins of the two nuclei, each of spin 3/2. These nuclei may mutually orient themselves to give any of seven different values for the combined spin (viz., -3, -2, -1, 0, 1, 

Explanations for Table 7 The concentration of Pb(C2Hs)4 in the appropriate solvent (in %) is given in column 1, included in ( ). The frequency at which the spectrometer was operated (in MHz) is also given in column 1 and is included in when different 

In the vapor state at 145 °C the proton chemical shifts of the CH2 and CH3 groups are equal within experimental error, and a shift of —44.5 0.5 Hz (downfield) relative to CH4 gas at 60 MHz was measured [3]. 

The internal chemical shift values, A5 = 5CH3-6CH2, of ethyl protons of Pb(C2Hs)4 In CCI4 and in hexamethyltriamidophosphate were reported to be +0.005 and -0.005 ppm, respectively [12]. 

For a relationship between the chemical shifts and the electronic charge of the C-H bonds of methyl groups In methyl and ethyl compounds of various metals, Including Pb(C2Hs)4, see [9]. 

The 6 Pb chemical shift of Pb(C2Hs)4 and of other organolead compounds broadly parallels the 6 Sn shift of analogous species and appears to be dominated by the paramagnetic contribution to the shielding [21]. 

Floch and S. Kovac, Coll. Czech. Chem. Comm., 1975,40,2845. 

Tanaka and Y. Tanaka, Chem. and Pharm. Bull. Japan), 1974, 22, 2546. 

4-position of A iV-dimethyl-2-nitro-aniline. N.m.r. provides a particularly direct technique for the study of the kinetics of proton exchange, exemplified in studies of arenethiols in AcOH.  

Both and F n.m.r. data have been employed in the assignment of 2,5-difiuorophenyl methyl sulphide as the structure of the product of reaction between MeS Na+ and 1,2,5-trifluorobenzene.  

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Gutowsky H S and Holm C H 1956 Rate processes and nuclear magnetic resonance spectra. II. Hindered internal rotation of amides J. Chem. Phys. 25 1228-34... 

Banwell C N and Primas H 1963 On the analysis of high-resolution nuclear magnetic resonance spectra. I. Methods of calculating NMR spectra Mol. Phys. 6 225-56... 

Specinfo, from Chemical Concepts, is a factual database information system for spectroscopic data with more than 660000 digital spectra of 150000 associated structures [24], The database covers nuclear magnetic resonance spectra ( H-, C-, N-, O-, F-, P-NMR), infrared spectra (IR), and mass spectra (MS). In addition, experimental conditions (instrument, solvent, temperature), coupling constants, relaxation time, and bibliographic data are included. The data is cross-linked to CAS Registry, Beilstein, and NUMERIGUIDE. 

Nuclear magnetic resonance spectra of 2-aminothiazole and of 2-imino-4-thiazoline were reported during the studies related to protomeric equilibria (125-127) ring protons in the former are centered at 6.48 and 7.14 ppm (internal Me4Si), while those in the latter are shifted upheld to 5.8 and 6.5 ppm (125). 

Nuclear magnetic resonance spectra of 2-alkylthio-4-amino-5-R-thiazoles have been recently described (135). 

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... 

NMR Characteristics of the nuclear magnetic resonance spectra of amines may be illustrated by comparing 4 methylbenzylamme (Figure 22 8a) with 4 methylbenzyl... 

Figure 7.10 Nuclear magnetic resonance spectra of three poly(methyl methacrylate samples. Curves are labeled according to the preominant tacticity of samples. [From D. W. McCall and W. P. Slichter, in Newer Methods of Polymer Characterization, B. Ke (Ed.), Interscience, New York, 1964, used with permission.]...

Physical Chemical Characterization. Thiamine, its derivatives, and its degradation products have been fully characterized by spectroscopic methods (9,10). The ultraviolet spectmm of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole yUd (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the piC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the patent cation and its major fragmentation ion, the pyrimidinylmethyl cation (16). 

The pKa values of 4-hydroxypyridine 1-oxide (51 52) and the methylated derivatives of both tautomeric forms indicate that the parent compound exists as a mixture containing comparable amounts of both forms in aqueous solution. Nuclear magnetic resonance spectra support this conclusion, but the ultraviolet spectra of the tautomeric compound and both alkylated derivatives are too similar to give information concerning the structural nature of the former. ... 

Nuclear magnetic resonance spectra of all four parent compounds have been measured and analyzed.The powerful potentialities of NMR as a tool in the study of covalent hydration, tautomerism, or protonation have, however, as yet received no consideration for the pyridopyrimidines. NMR spectra have been used to distinguish between pyrido[3,2-d]pyrimidines. and isomeric N-bridgehead compounds such as pyrimido[l,2- ]pyrimidines and in several other structural assignments (cf. 74 and 75). 

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