C—H bending bands

Quantitative calculations of the IMECs of the C=C stretching and C-H bending bands confirmed this trend (Table 1). Furthermore, for Ca2+ and Mg2+ cations the IMEC values exceed those for the free molecules, while for the Na+ ions there is little effect. This indicates a stronger polarization of the C=C bond in ji-complexes of propene with bivalent than with monovalent cations. As follows from Table 1 the IMECs of the C-H stretching vibrations of propene adsorbed by different cations are strongly decreased in comparison with the free molecule. The ratio of the IMECs for C=C and C-H stretching bands is increased for propene adsorbed by Mg2+ cations in comparison with the ratio obtained for the free molecule. 

These methods have been reviewed by Silas, Yates and Thornton [55]. In a PA-FTIR method Parker and Waddell also used the intensity of the 910 cm"1 butadiene band and ratioed it to the intensity of the 1450 cm 1 C-H bending band as a function of the % vinyl-butadiene [51]. The results can be expressed by a least squares linear regression equation over a range of 10%-60% vinyl-butadiene. 

The IR spectra of oxaziridines often show a band between 1430 and 1470 cm , which is assumed to be due to C—H bending (57JA5739). 

Absorption brought about by C-H bending is much more intense than that brought about by C=C stretching. The vibration band of C=C for cis forms is more intense than that for transforms. 

The spectra obtained from the chemisorption of methanol onto catalyst above 100°C indicated the progressive oxidation of methoxy species to formate via dioxymethylene/HCHO and finally to CO, CO2, and H2. Phenol adsorbed on the surface Lewis acid-base pair site and dissociated to phenolate anion and proton. The formation of phenolate anion and proton were discerned from the strong intense C-0 stretching vibration and the disappearence of phenolic 0-H stretching vibration, respectively. Importantly, there were series of definite low intensity bands between 2050 and 1780 cm" that were identified as the out-of-plane aromatic C-H bending vibrations [79, 84-85]. These bending vibrations are possible only if the phenyl ring of phenol is perpendicular to the catalyst surface. 

The IR spectra of methyllithium exhibited two C—H bending vibrational modes at 1480 and 1427 cm . Their assignment was again substantiated by significant isotopic shifts to 1100 and 1043 cm in the deuterium compound (Table 1). Only one weak band was observed for ethyllithium in the C—H deformation region at 1450 cm . Moreover, a new sharp peak was detected at 1385 cm and ascribed to the C—H symmetrical bending mode of CH3. Its absence in the IR spectrum of methyllithium is a further indication that free methyl groups exist only in ethyllithium. 

Figure 2 shows survey Raman spectra of the hcmopolymers, poly(methyl methacrylate)(PMMA.), poly(3-oximino-2-hutannone methacrylate)(pom), and poly(methacrylonitrile)(PMAN), and one terpolymer(P(M-0M-CN)) with a S/N ratio of about 10 1. Each of the polymers has a band specific to that polymer 8l2 dcm-1 (vg (C-O-C) for IMMA), 1622 hem" (Vg(C=N) for POM), and 2237 dcm l(vg(CHN) for PMAN). Additionally, there is an asymmetric C-H bending mode at 1 53 Acm l, common to all three homopolymers, which serves as an internal standard. These bands are indicated by arrows in Figure 2. A broad fluorescence background is evident, but it can be reduced to acceptable levels by exposure to high laser power for 10-30 minutes, depending on the sample. Residual background fluorescence may be due to the oximino chromophore itself. Figure 3 depicts an example of actual data for a 75 15 10 terpolymer with a S/N ratio of about 50 1.

C—H Bending Vibrations Cyclization decreases the frequency of the CH2 scissoring vibration. Cyclohexane absorbs at 1452 cm-1, whereas n-hexane absorbs at 1468 cm-1. Cyclopentane absorbs at 1455 cm-1, cyclopropane absorbs at 1442 cm-1. This shift frequently makes it possible to observe distinct bands for methylene and methyl absorption in this region. Spectra of other saturated hydrocarbons appear in Appendix B hexane (No. 1), Nujol (No. 2), and cyclohexane (No. 3). 

The most characteristic vibrational modes of alkenes are the out-of-plane C—H bending vibrations between 1000 and 650 cm-1. These bands are usually the strongest in the spectra of alkenes. The most reliable bands are those of the vinyl group, the vinylidene group, and the trans-disubstituted alkene. Alkene absorption is summarized in Appendix Tables D-l and D-2. 

C—H Bending Vibrations The C—H bending vibration of alkynes or monosubstituted alkynes leads to strong, broad absorption in the 700-610 cm-1 region. The first overtone of the C—H bending vibration appears as a weak, broad band in the 1370-1220 cm-1 region. 

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