Methylene wagging mode

If you use your hands at the end of your extended arms to represent the hydrogens for this motion, you will notice that it is necessary for you (the carbon atom) to wag or rotate your body to accomplish the motion. Hence, the spectroscopists call this mode the methylene wagging mode, Vw(CH2), which has frequencies ranging from 1308-1170 depending on the environment of the methylene unit and it has a different... 

Polyethylene (PE) is the most-studied example of rotational isomerism. The crystalline domains are made up of the all-trans conformer structure. Bands that are characteristic of rotamers in the amorphous phase are also present. The most intense of the amorphous absorptions are the methylene wagging modes at 1303, 1353 and 1369 cm . The TG conformation is correlated with the bands observed at 1303 and 1369 cm . The 1353-cm absorption band is assigned to the wagging of the GG structure. When PE is heated through its melting point, the concentration of the TG and GG conformations increases. However, the concentration of the TG conformation increases well below the melting point, and this increase indicates the formation of localized conformational defects in the crystalline polymer. 

The 725 cm" rocking mode doublet is presented in Figure 3. The peaks at 731 and 720 cm for this sample are approximately 15 times the intensity of the amorphous wagging modes. The 720 cm limiting frequency is assigned to long trans sequences in the amorphous and crystalline phases. For these samples, most of the methylene structures are in the crystal, and the band is associated with this phase predomi-... 

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 3.7. Assignment of iR peaks associated with scissoring and wagging modes of methylene groups of stearic acid seif-assembied from ethanol on 2-p,m silver particles ...

Figure 9.2 In-phase and out-of-phase methylene deformation and wagging modes in the chain (Snyder, 1960).

Fig. 2.12 Further examples of crystalline samples of long hain methylene sterns which demonstrate coupling of wagging modes.

The additional methylene vibrational modes are the wagging and rocking modes which are deformations in the z direction, i.e. perpendicular to the methylene groups. 

The bending vibrational modes of methylene group The top two dii rams frrocking modes. The bottom two dii rams show wagging and twisting modes. 

Progression of bands in solid state spectra, probably due to wagging and/or bending mode of vibration of the C—H bonds of methylene groups. The number of bands in the progression is indicative of chain length. 

Figure 7.55. IR bands used to monitor phase behavior of long-chain phospholipids. These bands, which are marked on spectrum, represent methyiene antisymmetric (of-) and symmetric (cf-F) C-H stretching, scissoring (5), and wagging (w) modes. Spectra shown are of fully hydrated diCIBPC the gel phase at -19° (solid curves) and in liquid-crystalline phase at 58° (dotted curves). Types of methylene-hydrogen motion associated with bands of interest are depicted. Reprinted, by permission, from R. G. Snyder, G. L. Liang, H. L. Strauss, and R. Mendelsohn, Biophys. J. 71,3186 (1996), p. 3188, Fig. 1. Copyright 1996 Biophysical Society.

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