Asymmetric stretching methylene

Alcohol 0-H stretch Olefinic C-H stretch Methyl C-H asymmetric stretch Methylene C-H asymmetric stretch Methyl and methylene C-H asymmetric stretch Lactone and ester carbonyl stretch (hydrogen bonded for 1711 and 1700 cm )... 

Primary-amine combination (N-H symmetric stretch + C-N stretch) Primary-amine combination (N-H symmetric stretch + deformation) Primary-amine combination (N-H asymmetric stretch + deformation) Methylene first overtones (C-H stretch)... 

In crystalline materials, with the alkane chains tightly packed and in an all-//cum conformation, the asymmetric stretch of the methylene groups va(CH2) shows at 2918 cm-1, whereas in liquid state, with disordered orientation of alkane chains and high concentration of gauche interactions, the position of this peak is shifted towards higher frequencies (2921-2924 cm-1). 

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... 

Asymmetrical stretching of a C—H bond in both a methyl and a methylene group. Both are present in iso-oetane and eentered at 2962 cm . ... 

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]. 

The weaker methylene peak in the first overtone region was said to be at 5671 + - 3 cm for linear hydrocarbons. This peak was thought to have contributions from both methyl and methylene groups (Tosi and Pinto), although others have assigned a 5680-cm band to be both the first overtone of the methylene symmetric stretch and of the asymmetric stretch shifted by Fermi resonance (Ricard-Lespade et al.). More recently, Parker et al. have discussed the origins of this peak in terms of local mode theory. 

C-H methylene C-H, associated with linear aliphatic R(CH2)nR C-H (2vCH2 asymmetric stretching and SCHj) combination Hydrocarbons, aliphatic... 

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