Wagging band

Figure 12.20 Raman spectra of l-ethyl-3-methylimidazolium liquid [C2CiIm] [Tf2N] showing the temperature-dependent SO2 wagging bands at —398 and —407 cm h According to Fuji et al. (Fujii, K., Fujimori, T., Takamuku, T, Kanzaki, R., Umebayashi, Y., and Ishiguro, S., /. Phys. Chem. B. 110, 8179-8183, 2006) the bands arise from different conformers of the [Tf2N]- ion, known also from crystal structures (Matsumoto, K., Hagiwara, R., and Tamada, O., Solid State Sci., 8, 1103-110 2006.) (Fujii, K., Fujimori, T., Takamuku, T., Kanzaki, R., Umebayashi, Y., and Ishiguro, S., /. Phys. Chem. B. 110, 8179-8183, 2006. With Permission.)...

The extensive studies of Snyder et al. (10) on the infrared spectra of hydrocarbons have also identified several CH2 wagging bands, which are nearly constant in frequency in the spectra of compounds with various chain lengths, that appear to be related to certain conformations, and are hence known as "defect modes. Changes in the relative intensity of these bands have been used to estimate the conformational disorder of the tails of micellar SDS (11), and the changes in packing of solid hydrocarbons as a function of temperature (12). 

The amorphous methylene wagging bands show a temperature behavior which is more amenable to discussion. The 1352 cm" band has been calculated to result from the deformation of the methylene isolated by the GG conformation (55,56). The intensity of this band increased at elevated temperatures relative to the other amorphous wagging modes as a consequence of the higher energy of its conformation (55,56). This was also observed in the present work for the slow-crystallized sample. However, increases for the rapidly quenched systems only occurred after... 

Table 2. Far infrared frequencies (in cm" ) and relative intensities for the c tjq>e torsional and wagging bands in methylamine obtained from ab initio calculations with the variable kinetic parameters.

The CH2 wagging bands are spread over a region between 1350 and 1180 cm", occurring as a characteristic progression of weak bands. They are best seen in the solid-phase spectra of long straight-chain compounds such as fatty acids [10). 

The CH2 twisting vibrations in CHy chains have frequencies dispersed over the same region as the wagging bands, as can be seen in the spectra of polyethylene [25], for example. The infrared intensity of these bands is weak, whereas in the Raman spectrum at about 1300 cm" the in-phase CH2 twist vibration is a useful group frequency. 

Fig. 1.29. Gas phase contours of absorption bands of pcra-xylene, propane, ethylene oxide, and ci>/S-chloroacrylonitrile measured in a 10-cm cell (unless noted otherwise) with a rock salt prism, (a)pora-Xylene at 7 mm Hg pressure in a 100-cm cell. The B type bands have a doublet structure and the A and C bands have a triplet structure. The C type band has a relatively strong central peak, (b) Propane at 679 mm Hg pressure. The A, B, and C type bands have the same structure as discussed for para-xylene, (c) Ethylene oxide s at 72 mmHg pressure except for the 800-900 cm band which is at 41 mm Hg pressure. The A and C bands have a triplet structure. The B type bands show four components, (d) c/j-j8-Chloroacrylonitrile at its vapor pressure at 25° C. In this planar molecule the out-of-plane CH wag band has a C type contour with the prominent central peak. This band is easily distinguished from nearby in-plane vibrations.

Rg. 5.8. CH2 wag band progression seen in the solid state infrared spectrum of sodium stearate. 

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