Methyl asymmetric bending

Methyl asymmetric bend Methyl symmetric bend Methylene symmetric bend Lactone C-O-C asymmetric bend Ester C-O-C asymmetric bend Lactone C-O-C symmetric stretch Ester C-O-C symmetric stretch Alcohol C-OH stretch Trisubstituted olefinic C-H wag... 

The donor-acceptor picture readily accounts for the observed methyl tilting and distortion.96 Figure 3.67 illustrates the asymmetric bending of each C—H bond of... 

Fig. 7 HREELS of the methylated Si(in). HREELS incident electron energy 2.84 eV, incident angle = exit angle = 60° from the surface normal. The full width at half maximum of inelastic peak = 7.6 meV. 2944 cm C—H stretching, 1423 cm CHj umbrella motion, 1268 cm CH3 asymmetric bending, 1099 cm Si—O stretching in Si02, 789 cm CH3 rocking,...

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.

The absorption band near 1375 cm-1, arising from the symmetrical bending of the methyl C—H bonds, is very stable in position when the methyl group is attached to another carbon atom. The intensity of this band is greater for each methyl group in the compound than that for the asymmetrical methyl bending vibration or the methylene scissoring vibration. 

FIGURE 2.19. Anisole. Aromatic C—H stretch,3067,3030,3005 cm . Methyl C—H stretch,2950,2843 cm". Overtone-combination region, 2000-1650 cm 1. C—C ring stretch, 1601,1501 cm-1. Asymmetric C—O—C stretch, 1254cm-1.Symmetric C—O—C stretch, 1046cm-1.Out-of-plane C—H bend,784,761 cm .Out-of-plane ringC—C bend, 699 cm-1. 

FIGURE 2.29. 2-Methyl-l,5-pentanediamine. N—H stretch, hydrogen-bonded, primary amine coupled doublet asymmetric, 3368 cm-1. Symmetric, 3291 cm. (Shoulder at about 3200 cm-1, Fermi resonance band with overtone of band at 1601 cm-1. Aliphatic C—H stretch, 2928,2859 cm-1. N—H bend (scissoring) 1601 cm-1. SsCH2 (scissoring), 1470 cm-1. C—N stretch, 1069 cm-1. N—H wag (neat sample), —900-700 cm-1. 

The bands due to methylene and methyl groups occur in the 1500-1350 cm" region. At around 1470 cm, there are bauds due to CH2 bending, with the number and frequency of these bands being dependent on acyl chain packing and conformation. While the asymmetric deformation modes of the CH3 group are obscured by the scissoring bands, the symmetric deformation mode appears at 1378 cm-i. 

The IR spectrum for low density PE in Figure 16.5 shows four high intensity absorption bands. The first band (A) corresponds to the symmetric and asymmetric stretchings of methyl and methylene groups. Then, symmetrical bending of methyl (B) and methylene (C) groups of the polymer... 

Spectral assignments have been made as follows. The spectra for p polarized IR for all the surfactants studied (Fig. l(a-f)) exhibit strong intensities for the methylene asymmetric stretch (d") at 2930 cm in agreement with the value observed in the IR spectrum, (2925 cm [45]. Peaks of moderate intensity are observed for the methylene symmetric (d ) and methyl symmetric (r" ") stretches at 2848 and 2872 cm" respectively. A weak methylene Fermi resonance (dpa) at 2900 cm resulting from interaction of an overtone of the methylene bending mode with the methylene symmetric stretch, is observed as a shoulder of the methylene asymmetric stretch. This can be compared to the methylene Fermi resonanee in polymethylene appearing in the IR (d" (it)FR) at 2898-2904 cm" and in the Raman (d" (0)FR) at 2890 cm" 1 [46,47]. 

---