Physical Method

Methods of filler pretreatment silane treatment of carbon black during mixing with rubber co-precipitatirm of cellulose xanthate and NBR latex  

Special considerations in conductive appUcations special conductive blacks must be employed in silver cmitaining gaskets galvanic corrosion is a problem, attention should be given to material with which shield is connected (potential difference), with zinc or aluminum casing nickel filled materials are preferred 

Major polymer applications modification of other polymers (e.g., HIPS and ABS), golf balls, tires, conveyor belts, hoses, seals and gaskets, rubberized cloth 

Important processing methods mixing, vulcanization, molding, extrusion, blow molding, injection molding 

Typical fillers carbon black, zinc oxide 

Physical Methods. H.p.l.c. procedures for the separation and assay of ubiquinone and homologues278-280 and of menaquinone cis- and fra/ts-isomers, 2,3-epoxides, and chain-length homologues281 282 have been described. A XH n.m.r. study has been reported283 of the location and motion of ubiquinones in perdeuteriated phosphatidylcholine bilayers. Other aspects of the interaction of ubiquinone with phospholipid monolayers have been studied.284 

Biosynthesis. An alternative pathway has been proposed for the early stages of the biosynthesis of the isoprenoid side-chain of ubiquinone in bacteria, via acetolactate rather than acetoacetate.285 3,4-Dihydroxy-5-hexaprenylbenzoic acid (248)286 and 

3-methoxy-4-hydroxy-5-hexaprenylbenzoic acid (249)287 have been identified as intermediates in the biosynthesis of ubiquinone-6 in Saccharomyces cerevisiae. In Escherichia coli, an enzyme-complex-bound pool of 2-octaprenylphenol (250) accumulated under anaerobic conditions, and was rapidly converted into ubiquinone-8 in air.288 The enzymic synthesis of o-succinylbenzoate,289 the conversion of this into its coenzyme A thioester, and the cyclization of this to 1,4-dihydroxy-2-naphthoic acid (251)290 have been demonstrated with bacterial cell-free preparations. Micrococcus luteus membrane fractions catalysed the prenylation of (251) by C15—C45 prenyl pyrophosphates en route to menaquinone.291 The chloroplast envelope has been reported as the site of (251) prenylation by phytyl pyrophosphate in phylloquinone biosynthesis.292 Several genetic studies of bacterial menaquinone biosynthesis have been described.293-295 Two papers report the formation of plastoquinone (237) in spinach296 and lettuce297 chloroplasts. 

Kemmerling, and G. Schultz, Arch. Biochem. Biophys., 1980, 204, 544. 

The Table beginning on p. 271 lists steroids which have been the subject of A -ray crystallographic studies during the year. Comment on the conclusions is limited to only a few of the compounds. 

Physical methods for size determination are mainly related to the use of X-ray based diffraction, scattering and absorption techniques, microscopy, and magnetic measurements. Physical and chemical methods may be combined, for example, in the use of infrared spectroscopy coupled to the use of probe molecules such as CO to determine the fraction of exposed metal atoms. However, as Chp 3 has already dealt with characterisation of supported metal systems by X-ray absorption and infrared spectroscopies in some detail, they will not be included here. 

As indicated above, physical methods provide a means by which the dispersion is derived from measurement of particle size. In actual fact, the value referred to as particle size when obtained by X-ray diffraction, should be termed crystallite size as the particle may contain several crystallites and the parameter being measured is the effective length in the direction of the diffraction vector, along which there is coherent diffraction. Additionally, for the case of X-ray diffraction, the value obtained is inherently an average value given that the sample will contain a distribution of particle sizes and the quantity to be determined from the XRD pattern is the 

On this basis, a representation of the magnetisation (that can be obtained in general with magnetometers or can be considered proportional to the ferromagnetic resonance signal obtained in ESR spectrometers) vs. temperature yields thermomagnetic curves as a function of the particle volume.11 From comparison of experimental data with such curves, an estimation of the mean particle size can be obtained. Size distributions can 

On the other hand, estimates of the metal dispersion have been achieved by use of HREM.26 Thus, such parameters can be inferred from the particle size distribution by assuming a certain metal particle geometry (equations 

As indicated above, physical methods provide a means by which the dispersion is derived from measurement of particle size. In actual 

The intensity of the diffracted radiation is related to the square of the atomic number and hence for the case of supported metal catalysts, the lower limit of sensitivity is likely to fall around 0.3 to 0.8 wt% loading. Additionally, once the crystallite size falls below ca. 2-4 nm, the diffraction line becomes so broad and 

In addition to line broadening, metal particle size for a supported metal catalyst may be determined from X-ray scattering techniques 

Transmission electron microscopy (TEM) is a powerful and routinely employed technique for the analysis of particle size and morphology in supported metal catalysts. A more thorough description of its uses and applications is provided in Chapter 3, 

Physical methods to characterize the mixing efficiency are based on the use of an inert tracer, which differs in color, conductivity, or optical density from the main 

In a more precise method of investigation, the local concentration in a controlled volume is considered. This allows determining the concentration fluctuations referred to the mean. 

It is evident that the degree of mixing measured experimentally will depend on the spatial resolution of the probe used to estimate the local concentration in the mixture. Depending on the kind of application, a decrease in the length scales on which these variations are present or reduction in their amplitude or both are desired. 

There are several limitations to optical techniques as described in the following  

The principle of competitive chemical reactions is based on the fact that when the characteristic mixing time and characteristic reaction time are of the same order of magnitude, two processes will compete resulting in lower consumption rate of 

Important physical properties associated with polymers (or membranes) such as the glass transition temperature, their crystallinity and density can be determined by a large number of techniques. Some of these will be described briefly to enable a better understanding to be obtained concerning permeability through nonporous polymeric films. 

Differential Scanning Calorimetry (DSQ and Differential Thermal Analysis (DTA) are in 

Examples of physical-property changes that can be used for this purpose are as follows  

In addition to chemical composition (concentration of a species) and properties in lieu of composition, other quantities requiring measurement in kinetics studies, some of which have been included above, are  

In the physical methods the mixing of an additive, which differs in temperature, concentration or density (refraction index) from the vessel contents, is foUowed by measuring the temperature, the electrical conductivity, the pH-value or by Schlieren optics. Other methods worthy of mention are  

If the homogenization process proceeds during the temporal course of the temperature equalization, a thermographic method (LCT) can be used, which is based on the coloring of thermochromatic liquid crystals [645]. 

The mixing time can be determined by chemical means, if the tank contents is mixed with a reaction component and the component to be added is mixed with a (1 4- x)-fold equivalent of the second reaction component, so that after intimate mixing the two reaction partners react with one another. The disappearance of the reaction partner is shown by a color indicator, which experiences a sudden color change. ( Method of the last color change is used, in contrast with decolorizing reaction which is proportional to the degree of conversion, see e.g. Kappel [262]). The redox reactions of thiosulfate with iodine (indicator starch) and the neutralization of sodium hydroxide with sulfuric acid (indicator phenolphthalein) have been found to be simple fast ionic reactions, suitable for this purpose. 

The black/colorless endpoint of the redox indicator starch has an advantage over pH-indicators, in that the disappearance of the dark color in thick layers in a red/ yellow or blue/yellow color change is sometimes not clear [205]. Phenolphthalein with its color change red/colorless is less suitable for measurement purposes, since the color at high pH-values bleaches due to a slow secondary reaction. In mixing experiments with tap water time lag has been also observed [51]. 

The relationship between the maximum amount of the relative deviation dmax and the ratio x — Ha/mb of the normalities of both reaction partners before they are brought together A - additive B - receiver) can be established as follows. Upon color change both reactands are present in stoichiometric equivalence (e). For the local volume fraction the following then applies 

Physical or mechanical methods of cell disruption are the most widely researched in terms of containment. The underlying principle is either by breakage of the cell wall by mechanical contact, the application of liquid or hydrodynamic shear forces, or the application of solid shear forces. Cell disruption by non-physical methods generally involve simple operations which may be carried out in large tanks or vessels, which may or may not require agitation. 

Bead mills are generally operated at near ambient pressure. When disrupting very thick cell pastes, there may be a slight build up of pressure in the vessel, but it is unlikely to exceed 0.2 bar, so bead mills are unlikely to cause aerosols to be released during operation. In the event of seal 

The earliest devices to employ this principle were the French Press and the Chaikoff Press Both these devices are relatively crude and simple which can only disrupt small batches of cell suspensions. The next stage in the development was the introduction of dairy industry homogenisers of which the Manton-Gaulin 15M is a typical example. 

APV-Gaulin International (Hilversum, NL) manufacture and supply a wide range of high pressure cell disrupters. Capacities range from 40 to 6000 litres per hour with operating pressures up to 1100 bar. The 

Bran and Luebbe (GB) Ltd, Brixworth (part of the Alfa Laval group) supply high pressure homogenisers which are also similar in design to the 

Although all the physical methods of purification, which comprise the various forms of distillation and of crystallisation, as well as adsorption, can be done in a high vacuum system, the only ones for which this is generally worthwhile are crystallisation without solvent and its sophisticated version zone-refining, and adsorption. Of course, degassing cannot be done otherwise than on a vacuum system. 

In some systems an impurity may partition itself in such a way that it is swept to the top of the ingot, and of course both types of impurity may occur in the same material. In such cases only the middle part of the ingot has the required purity. (The author thanks Prof. J. N. Sherwood for some personal advice on this point.) 

Some compounds expand so much during the melting and freezing cycles 

Adsorption. The process of adsorption involves the partitioning of the adsorbed substance between the bulk phase in which it is dissolved and the surface of the adsorbant, and it is a reversible, equilibrium process, unless the adsorbed species is transformed or bound chemically the use of solid reagents to trap impurities by chemical reaction will be discussed in the following section. 

It is generally found that the best adsorbants have a relatively small 

The principal shortcoming inherent in all of the methods discussed in the previous Section is that the system under study is necessarily subjected to some chemical perturbation. Although this perturbation is often a minor one, nevertheless, in many instances (particularly when biochemically important systems are concerned), antj chemical perturbation whatsoever is unacceptable. Under these conditions, there is no choice but to resort to instrumental methods (discussed in depth in this Series by Coxon ), of which there are three distinct categories at present. 

Clearly, it is always advantageous to record a n.m.r. spectrum at as high a field as possible. An excellent illustration of this factor is the re-investigation (at 100 MHz) of the H n.m.r. spectra of glycopyranose peracetates, which had been first studied with a 40-MHz instrument. The spectra shown in Fig, 4 for myo-inositol at 60, 100, and 220 MHz exemplify this point. 

Nevertheless, even at 360 MHz, assignment of the H n.m.r. spectra of higher oligosaccharides, and polysaccharides, is still a formidable problem. For example, Perlin and coworkers, with a 220-MHz instrument, made a study on heparin that led only to the assignment of the anomeric protons again, it is interesting that, on those occasions when it is possible to esterify the substance fully, prior to study, the H n.m.r. spectra show a substantial increase in dispersion.However, it seems reasonable to conclude that, at least for the present, detailed interpretations of the H n.m.r. spectra of polysaccharides are unlikely to be achieved, even were the expensive equipment needed for such measurements to become more widely available. 

In view of the present limitations on the magnetic field-strengths obtainable from superconducting solenoids, it is fortunate that a wide variety of double-resonance experiments can be performed 

Any double-resonance experiment can be performed in either of two sweep-modes, namely, field-sweep (when the spectrum is scanned by 

Only a brief outline of physical methods will be attempted in this section, and no reference will be made to instrumentation. Existing literature on the subject is enormous and techniques continue to diversify. Only appropriate specialised works can be consulted for full information. Today, physical methods are frequently employed alongside chemical methods for analysis of phosphorus-containing compounds. 

The term analysis used in the broadest sense can include 

Detection of elemental P and measurement of its concentration in a given sample 

Identification of, and estimation of, specific P compounds in a given sample 

Caio(P04)g(OH)2, hydroxyapatite Phosphomolybdic acid (Sonnenscheims reagent) 

The testing methods are divided into two groups physical methods and chemical and instrumental analysis. Within the group, the testing methods are discussed in alphabetic order according to the same pattern. 

Basically there are two broad synthetic methods [74—76] for NMs - physical methods and chemical methods. 

Several physical methods are currently in use for the synthesis and commercial production of NMs which are as follows  

Significant developments relating to the application of the physical methods for structure determination of carbazole alkaloids after 1977 (18) are briefly summarised here. 

These use a physical property dependent on concentration and must be calibrated, but are still much more convenient than chemical methods. Measurement can often be made in situ, and analysis is often very rapid. Automatic recording gives a continuous trace. It is vital to make measurements faster than reaction is occurring. 

The following problems illustrate typical physical methods used in the past. 

Pressure changes in gas phase reactions Worked Problem 2.5 

Question. Which of the following reactions can be followed in this way and why  

Which reaction would give the largest change in total pressure and why Suggest an alternative method for reaction 3. 

analyses are replaced by the continuous acquisition of a properly provided by the method. We then need to know how to relate this quantity to the fractional extent or the rate of the reaction. There are two categories of methods  

This method is used in the gas phase when there is a change in the number of moles of gas due to the reaction. The total pressure is measured in a closed gas chamber. 

We start from a stoichiometric mixture of reactants, which means we have 

This method applies to gas-phase reactions or to heterogeneous reactions that lead to a change in gas amount, such as the decomposition of a carbonate. 

This pressure will vary with the composition of the mixture, which means it varies with the fractional extent of the reaction. This method only applies to gases and requires prior calibration. 

During the early structural studies 60 MHz H-n.m.r. spectroscopy and electron impact mass spectroscopy were the most important physical tools used. Despite the great amount of information obtained by these physical methods, structural elucidation relied heavily on chemical transformations, 

In recent years higher field H-n.m.r. spectroscopy and new mass spectroscopic methods (chemical ionisation, field desorption, FAB and Mikes technique) became available. Recently Baldwin etal. (2) applied some of these new mass spectroscopic techniques to the structure determination of some bruceolides. A detailed C-n.m.r. study of a number of quassinoids has been published (Si) and C-n.n.r. data have since then been recorded in most of the papers dealing with constituents of Simaroubaceae. X-Ray analysis has also become more accessible and structures of many quassinoids are now being established by this method. 

HPLC was used for the separation of mixtures of quassinoids 66,96) and recently a quantitative HPLC analysis of the quassinoids from Simarouba glauca has been described (59). Enzyme-linked immunosorbent assays for quassin (85) and a number of other quassinoids have been carried out (95,97). 

The remark has been made that compounds of tin can be studied by more techniques than those of any other element. The fact that it has more stable isotopes that any other element gives it very characteristic mass spectra, and isotopic labelling can be used to interpret vibrational spectra, and for spiking samples in trace analysis two of the isotopes have spin 1/2 and are suitable for NMR spectroscopy, and their presence adds information to the ESR spectra of radical species. Further, the radioactive isotope 119mSn is appropriate for Mossbauer spectroscopy. The structural complications that are referred to in the previous chapter have therefore been investigated very thoroughly by spectroscopic and diffraction methods, and structural studies have always been prominent in organotin chemistry. 

In the sections that follow, the basic theory of these techniques will be discussed only insofar as it is specially relevant to organotin compounds. It must always be borne in mind that the structures of organotin compounds which carry functional groups may be dependent on the physical state (gaseous, solid, or liquid), and, when the compounds are in solution, on the nature of the solvent and on the concentration. For example, the Sn-Cl stretching frequency in the far IR spectra of trimethyltin chloride in solution can be correlated with the donor number of the solvent. Caution must therefore always be exercised in attempting to quote typical values for properties such as vibrational frequences or NMR chemical shifts. 

Typical vibrational frequencies for organotin compounds are tabulated by Neumann,4 Poller,5 Omae,6 Harrison,2 and Nakamoto3 and data on individual compounds can be found in the relevant volumes of Gmelin.7 

Tetraorganotin compounds, R Sn, show little tendency to be other than tetrahedrally 4-coordinate, and their vibrational frequencies are not dependent on the physical state (Table 2-1). The force constants in Me4Sn are/Sn-C 2.19, and/C-H 4.77 N cm F8 The CF3-Sn bond is longer and weaker than the CH3-Sn bond [220.1(5) pm in (CF3)4Sn and 

Organotin Chemistry, Second Edition. Alwyn G. Davies Copyright 2004 Wiley-VCH Verlag GmbH Co. KGaA. ISBN 3-527-31023-1 

The determination of specific surface area of soils and soil coUoids is of great importance in characterizing the reactivity of a sample, among other factors. However, it is actually an operational concept, because the A5 value depends on the experimental method employed, as it will be shown in Section 7.6.4.I. The underlying fact is that the effective area available for a particular reaction or process is dependent on the reactants and/or external factors involved. The experimental methods can be broadly classified into three categories (Sposito 1984) physical methods, positive adsorption methods, and negative adsorption methods. 

Physical methods classically included XRD (Section 7.3.1) and electron microscopy (Section 7.5.1) to determine the shapes and dimensions of typical particles compute their area, A and calculate the crystallographic specific surface area, knowing the density of the particles, p  

Among other methods, one that lies between physical and adsorption classes is the Hg porosimeter, in which the sample is placed in contact with Hg, pressure is applied to fill the pores with the liquid metal, and the amount of Hg required is measured (Arnepalli et al. 2007). 

It is worth noting that, for low-resolution, electron-bombardment, 

Reviews of 19F-n.m.r. spectroscopy of specifically fluorinated carbohydrates have been included in a number of articles, namely, by Inch271 in 1969 and 1972 (Ref. 272), simultaneously by Fields273 and Bentley274 in 1972, by Kotowycz and Lemieux275 in 1973, by Emsley and coworkers,278 who dealt, exclusively with, 9F coupling constants, in 1976, and by Wasylishen277 in 1977 (see also, Refs. 278-280). 

No simple rationalization for the observed values of the 19F resonances could be made for the peracetylated 2-deoxy-2-fluoro-D-gIuco-and -manno-pyranosyl fluorides, apart from the fact that the anomeric fluorine substituent always gives the lower field-resonance of the two198 this should, however, be compared with the explanation described287 (see later in this Section) for the observed differences in 19F 

Stereospecificity was also encountered in long-range interactions. For 3-deoxy-3-fluoro-D-glucopyranose, the a anomer resonated to 

It has also been observed281 that, for a number of fluorinated monosaccharides, geminal 19F- H coupling-constants for the pyranose series are larger when the fluorine substituent is axially rather than equatorially disposed. Exceptions to this generalization were subsequently found, as in the virtually identical value of/F 2, H-2 for peracetylated 2-deoxy-2-fluoro-a-D-gluco- and -manno-pyranosyl fluorides.71 

The abbreviations Pm, PIV, and Pv refer to the co-ordination number of phosphorus and the compounds in each subsection are usually dealt with in this order. A number of relevant theoretical and inorganic studies are included in this chapter. In the formulae the letter R represents hydrogen, alkyl, or aryl, X represents electronegative substituents, Ch represents the chalcogenides (usually oxygen and sulphur), and Y and Z are used to indicate a wide variety of substituents. 

The very high accuracy which may be obtained by the pulsed Fourier transform method has been demonstrated using o-phenylene phosphorochloridite.1 

Comparison of the -n.m.r. spectrum of 3-0-(methylsulfonyl)-/3-maltose heptaacetate (31) with that of /3-maltose octaacetate showed only one divergence, —0.34 p.p.m. upfield of the H-3 resonance, indicative of the location of the methylsulfonyloxy group on C-3. A similar comparison of H-n.m.r.-spectral parameters as between methyl 4 -0-(methylsulfonyl)-/3-maltoside hexaacetate and methyl /3-maltoside heptaacetate revealed that the methylsulfonyloxy group in the former compound is located on C-4, as the H-4 resonance appeared —0.3 p.p.m. to higher field than the H-4 resonance for the heptaacetate.66 In the H-n.m.r. spectrum of methyl 3-azido-3-deoxy-/3-maltoside heptaacetate, the H-3 resonance appeared at 1.70 p.p.m. to higher field of 

High-resolution, H-n.m.r. spectra of trityl ethers of maltose and its derivatives have been described.45,68 166 In the H-n.m.r. spectrum of methyl 2,2, 3, 4 -tetra-0-acetyl-3-0-(methylsulfonyl)-6,6 -di-0-trityl-/3-maltoside (68), the chemical shifts of methine protons (H-2, H-2, H- 

Raney nickel catalyst. Methyl a-D-glucopyranoside was fully deu-terated at carbon atoms 2, 3, 4, and 6, to afford 71, by treatment with 

Octa-O-acetyl- 0-maltose1M 6 -Chloro-6 - deoxy-a- maltose 0 6 -Chloro-6 - deoxy-0- maltose10 6,6 -Dichloro- 6,6 -dideoxy- a-maltose90 6,6 -Dichloro- 6,6 -dideoxy- / -maltoseM 

507 and 483, corresponding to 76 (M+—OAc—HC1) and 77 (M+—OAc—OAc), of which an analog of the former had been observed24 in the mass spectrum of methyl 2-0-acetyl-3,6-dichloro-3,6-dideoxy-4-0-(2,3-di-0-acetyl-4,6-dichloro-4,6-dideoxy-a-D-galactopy-ranosyl)-/3-D-allopyranoside (36). 

The volatile compounds in the first four entries were suitable for gas-phase electron diffraction studies. Their octahedral (entries 1-3) and trigonal bipyramidal (entry 4) geometries are shown in formulas (XXXIV) and (XXXV). In each case, it was found that the carbonyl 

Strangely, the shortest Si-M distance reported (entry 5) is also in a formally d° situation. The compound (XXXVII) is prepared by the reaction of KSiH3 and (V-CjHs TiCl in glyme the reason for its anomalously short Si-Ti bond is not clear. 

There has been much interest in the possibility of Si- -H- M bridging, first suggested in connection with the compound (Ph2Si) Re2(CO)sH2 (entry 18) (173, 250). Although the hydrogen atoms were not located, infrared spectral evidence supported a structure (XXXVIII), with some H- Si interaction. However, a series of related compounds (XXXIX)-(XLI) (entries 16, 17, and 19) have now 

made by irradiating a mixture of HSiPhCl2 and Re2(CO)i0 (248, 251), appears to involve a Re- H- Re bridge, but no details of the structure apart from the Si-Re bond length have yet been published. 

Among the iron compounds, several of the type (R3Si)2FeH(CO)(Cp) (entries 23, 24, and 29) possess the structure shown in (XLIV), with trans RsSi groups. In the case when R3 = MeF2, d(Fe-H) is about 150 pm, while the Si H distance (206 pm) is not thought to correspond to significant interaction. 

The quantity of fat from the cocoa shell that ends up in the cocoa butter can be measured by testing with p-dimethyl-aminobenzaldehyde, which reacts with dried fruit pulp adhering to the shell. The reaction gives an intense fluorescence and has been used with TLC and fluorescence spectrophotometry (Kleinert, 1964). Shell fat is softer than nib fat because it contains higher levels of linoleic acid (18 2) and its presence softens the butter (Timms and Stewart, 1999). However, its presence can be usually due to poor separation of shell from nib rather than direct adulteration. 

A fluorescence under UV illumination of an unidentified compound separated by TLC has been used to detect 5% kokum (possibly unrefined) in mixtures with cocoa butter (Deotale el al., 1990). Identification of this compound and its analysis by more specific techniques might be used to improve current methods of quantifying CBEs in chocolate. 

Nuclear magnetic resonance (NMR) can be used as a rapid alternative to differential scanning calorimetry in the determination of the solid fat content and studies on the melting behaviour. The determination is based on detection of the different populations of protons in solid and liquid phases, which indicates the hardness of the fat. Hernandez and Rutledge (1994b) used low resolution pulse NMR to compare melting curves of roasted and non-roasted cocoa butters from Africa, Indonesia and South America. Discriminant analysis techniques showed 

Infrared and Raman spectroscopy techniques have also been shown to be of value in determining oil authenticity, particularly when based on the degree of saturation (Aparicio and Baeten, 1998 Bertran et al., 2000), but these methods have not yet been substantially applied to cocoa butter and confectionery fats. 

Nuclear magnetic resonance spectroscopy has emerged as the most powerful tool for elucidating the molecular structures of cyclophos-phazene derivatives in solution. Proton NMR spectroscopy has been widely used because of its easy accessibility. The recent development of sophisticated instrumental facilities and the application of broadband proton decoupling have greatly improved the quality and usefulness of the 31P spectra (252) of cyclophosphazenes, and it is likely that this technique will become increasingly popular in the future. Fluorine NMR studies are useful for deducing the structures of fluorocyclophosphazenes, and the potential of this technique has been demonstrated in recent years (209, 210, 213, 307, 308, 343). 

Proton NMR spectroscopy is particularly useful for determining the disposition of substituents in aminohalogenocyclophosphazenes. Four criteria are utilized for this purpose (a) the number of proton environments, (b) the value of 3J (P—H), (c) the relative chemical shifts (geminal versus nongeminal and cis versus trans), and (d) the presence or absence of virtual coupling (see detailed discussion in the following). 

The three isomeric trisdimethylaminotrischlorocyclotriphospha-zenes, cis-, trans-, and gem-N3P3Cl3(NMe2)3, have been identified by the observation of one, two, and three dimethylamino doublets (coupling to 31P), respectively, in their proton NMR spectra. In addition, the magnitude of 3 J (P—H) in PCl(NMe2) and =P(NMe2)2 

The 1H NMR study of dimethylamino and/or methoxy derivatives of partially substituted cyclophosphazenes has been utilized to obtain 

The 19F NMR spectra of fluorodimethylamino derivatives of cyclotri-and cyclotetraphosphazenes confirm the structures assigned to isomeric products on the basis of 1H NMR data, although a detailed analysis of the 19F spectra of many derivatives could not be made (209, 210, 213, 307, 308). Some typical spectra are shown in Fig. 12. The structures of many chlorofluoro- (108,163,223,224), bromofluoro- (120), and phenylfluorocyclophosphazenes (32, 33,116) have been established mainly on the basis of 19F NMR data. Also 19F NMR data for a series of fluoroalkylamino- (113, 114, 196, 197, 327), fluoroalkyl- (354), and fluoroalkoxycyclophosphazenes (441) have been reported. 

The difficult task of determining the preferred conformations of nucleotides and other complex naturally-occurring organophosphorus compounds has been studied by combined and P n.m.r. spectroscopy assisted by MO calculations. A review of P n.m.r. spectroscopy has been published.  

Totally absorbing material is heated by incident irradiation (bolometer). A relationship between intensity and temperature effects exists. Since temperature measurement are very sensitive, this effect is used to determine intensities. Semiconductor detectors either use the internal or external photoeffect [117,118]. In a photodiode, an incident photon causes a photocurrent by charge separation. It can be amplified and depends linearly on the number of incident photons. 

In photocathodes or photomultipliers the incident photons force electrons to leave the material. This external photoeffect can be calibrated and amplified by acceleration and multiplication of the electrons in multi-electrode arrangements (dynodes). These devices have very short response times and can be successfully used to control the stability of a light source. Therefore such devices are frequently included in commercially available set-ups. An example is given in Fig. 4.32 combining an irradiation source with a measurement set-up. This is commercially available [119] and allows simple control of a photoreaction. However, due to geometry and inhomogeneity of the sensitive layer of the photodiode, non-homogeneous irradiation can cause errors. 

These thermoelements, photoelements, and other physical measurement devices can cause some problems for the photochemist  

Irradiation set-up in wiiich the photoreaction is controlled by spectroscopy. The intensity of the radiation source is monitored by a physical device measuring photocurrent 

These facts makes it obvious that physical mediods are perfect to control 

More recently, Ilu et al. have demonstrated that the quantity and dimensions of the Ag nanoparticles can be controlled by varying the y-radiation dose appUed to the silver nitrate solution, with good batch-to-batch reproducibility [29], These authors also highlighted the fact that the nanoparticles produced were clean -that is, no polymer or surfactant is required to stabilize them. 

In a similar method, the trisodium citrate can be replaced by PVP. In a study carried out by Shin et al. [30], transmission electron microscopy (TEM) findings showed that both the amount and the molecular weight of the PVP in the irradiated solution affected the average size of the nanoparticles produced. A three-step mechanism for the formation of these nanoparticles has been postulated. First, the silver ions interact with the PVP, after which nearby silver atoms that have been reduced by y-radiation aggregate to form primary particles. Finally, nearby primary particles coalesce to form larger aggregates which are termed secondary particles. 

Another report which involves the use of PVP describes the comparison of silver nanoparticles prepared by y-radiation and by chemical reduction [31]. It was reported that the y-radiation strategy produced silver nanoparticles with a narrower size distribution, with the final size also being tuned by varying the concentration of the silver nitrate precursor. In contrast, the chemical reduction method does not allow such ease in tuning the particle size. 

Microwave irradiation has also been used to prepare silver nanoparticles, as described by Yin et al. In this method, the large-scale production of silver nanoparticles was achieved from a silver nitrate and trisodium citrate solution, in the presence of formaldehyde as the reducing agent [33]. 

Tan et al. have recently reported the UV-assisted reduction of silver ion in polyamine solutions, namely branched poly(ethyleneimine) (BPEI), at low concentrations of HEPES, that resulted in the formation of positively charged Ag nanoparticles [35]. It was reported that the BPEI silver nitrate HEPES molar ratio 

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In this manner, the KuQp of a petroieum cut can be calcuiated quickly from readily avkilable data, i. e., the specific gravity and the distillation curve. The A //np value is between 10 and 13 and defines the chemical nature of the cut as it will for the pure components. The characterization factor is extremely Va luable and widely used in refining although the discriminatory character of the Kuqp is less than that obtained by more modern physical methods described in 3.2 and 3.3. 

More than hundreds of physical methods, thousands of different types of units are used for NDT and TD currently and the expenses for all these activities are many tens billions of USD per year. 

The following table 1 gives brief presentation of physical methods used for this or that diagnostic procedure. 

B. W. Rossiter and R. C. Baetzold, Physical Methods of Chemistry, 2nd ed., Vol. IXA, Investigations of Surfaces and Interfaces, Wiley-Interscience, New York, 1993. 

Oscarson J L and Izatt R M 1992 Calorimetry Physical Methods of Chemistry Determination of Thermodynamic Properties 2nd edn, vol VI, ed B W Rossiter and R C Baetzold (New York Wiley)... 

Boerio-Goates J and Callanan J E 1992 Differential thermal methods Physical Methods of Chemistry... 

Molecular Weight Determinations by Physical Methods. Vapour Density. Victor Meyer s Method. 

Separations based upon differences in the physical properties of the components. When procedures (1) or (2) are unsatisfactory for the separation of a mixture of organic compounds, purely physical methods may be employed. Thus a mixture of volatile liquids may be fractionally distilled (compare Sections 11,15 and 11,17) the degree of separation may be determined by the range of boiling points and/or the refractive indices and densities of the different fractions that are collected. A mixture of non-volatile sohds may frequently be separated by making use of the differences in solubilities in inert solvents the separation is usually controlled by m.p. determinations. Sometimes one of the components of the mixture is volatile and can be separated by sublimation (see Section 11,45). 

Braude and Nachod, Determination of Organic Structures by Physical Methods, 1955 (Academic Press). 

The differentiation of bridged nonclassical from rapidly equilibrating classical carbocations based on NMR spectroscopy was difficult because NMR is a relatively slow physical method. We addressed this question in our work using estimated NMR shifts of the two structurally differing ions in comparison with model systems. Later, this task... 

Although the nitronium ion cannot be detected by physical methods in these media, kinetic studies using these solutions have provided compelling evidence for the formation and effectiveness of this species in nitration. 

Ridd, J. H. (1963). Physical Methods in Heterocyclic Chemistry, vol. i, ed. A. R. Katritzky. London Academic Press. 

Faulkner, L. R. Electrochemical Characterization of Chemical Systems. In Kuwana, T. E., ed.. Physical Methods in Modern Chemical Analysis, Vol. 3. Academic Press New York, 1983, pp.137-248. 

Buck, R. P. Potentiometry pH Measurements and Ion Selective Electrodes. In Weissberger, A., ed.. Physical Methods of Organic Chemistry, Vol. 1, Part IIA. Wiley New York, 1971, pp. 61-162. Cammann, K. Working with Ion-Selective Electrodes. Springer-Verlag Berlin, 1977. 

The copolymer composition equation relates the r s to either the ratio [Eq. (7.15)] or the mole fraction [Eq. (7.18)] of the monomers in the feedstock and repeat units in the copolymer. To use this equation to evaluate rj and V2, the composition of a copolymer resulting from a feedstock of known composition must be measured. The composition of the feedstock itself must be known also, but we assume this poses no problems. The copolymer specimen must be obtained by proper sampling procedures, and purified of extraneous materials. Remember that monomers, initiators, and possibly solvents are involved in these reactions also, even though we have been focusing attention on the copolymer alone. The proportions of the two kinds of repeat unit in the copolymer is then determined by either chemical or physical methods. Elemental analysis has been the chemical method most widely used, although analysis for functional groups is also employed. 

Most of the experimental information concerning copolymer microstructure has been obtained by physical methods based on modern instrumental methods. Techniques such as ultraviolet (UV), visible, and infrared (IR) spectroscopy, NMR spectroscopy, and mass spectroscopy have all been used to good advantage in this type of research. Advances in instrumentation and computer interfacing combine to make these physical methods particularly suitable to answer the question we pose With what frequency do particular sequences of repeat units occur in a copolymer. 

The choice of the best method for answering this question is governed by the specific nature of the system under investigation. Few general principles exist beyond the importance of analyzing a representative sample of suitable purity. Our approach is to consider some specific examples. In view of the diversity of physical methods available and the number of copolymer combinations which exist, a few examples barely touch the subject. They will suffice to illustrate the concepts involved, however. 

J. W. S. Heade and R. Muldith, eds.. Physical Methods of Investigating Textiles, Interscience PubHshers, Inc., New York, 1959. 

The preferred quantitative deterrnination of traces of acetylene is gas chromatography, which permits an accurate analysis of quantities much less than 1 ppm. This procedure has been highly developed for air poUution studies (88) (see Airpollution control methods). Other physical methods, such as infrared and mass spectroscopy, have been widely used to determine acetylene in various mixtures. 

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