Wagging structure

To the extent that the segmental friction factor f is independent of M, then Eq. (2.56) predicts a first-power dependence of viscosity on the molecular weight of the polymer in agreement with experiment. A more detailed analysis of f shows that segmental motion is easier in the neighborhood of a chain end because the wagging chain end tends to open up the structure of the melt and... 

Structure Symmetry Ring breathing C-H stretch CH2 scissoring CHi wagging Ref. 

Systems involving more mass points are capable of more complex vibrations, since the vibrational modes may involve several to many atoms and all three dimensions are available for vibrational movements. Vibrations where primarily the distances along the bond axis between the involved atoms change during the vibration are called valence vibrations. Vibrations causing a deformation of a bond angle are referred to as deformation vibrations. Deformation movements can also rock , wag or twist a molecular (sub-) structure (Figure 1). 

If we accept structure 1 (Scheme 3) as possible, the position of the two CH motions, the symmetrical mode above the asymmetrical mode, would not be in accord with all data of comparable structures. Moreover, the two bending motions observed at 714 and 480 cm are very unlikely due to a rocking or wagging motion of the CH2 group. Hence, structure 1 can be ruled out. 

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.)...

In allene structures, strong absorption is observed near 850 cm-1, arising from =CH2 wagging. The first overtone of this band may also be seen. Some spectra showing alkene features are shown in Appendix B trichloroethylene (No. 12) and tetrachloroethylene (No. 13). 

Goldman, Y.E. (1998) Wag the tail structural dynamics of actomyosin. Cell 93, 1-4. 

Structure Symmetry King breathing C-H stretch ch2 scissoring CH, wagging Ref. 

Cyclization of squalene is via the intermediate squalene-2,3-oxide (Figure 5.55), produced in a reaction catalysed by a flavoprotein requiring O2 and NADPH cofactors. If squalene oxide is suitably positioned and folded on the enzyme surface, the polycyclic triterpene structures formed can be rationalized in terms of a series of cycliza-tions, followed by a sequence of concerted Wag-ner-Meerwein migrations of methyls and hydrides... 

It is noticeable that the NRG theory developed here furnishes two different groups for the double rotation in planar pyrocatechin (or acetone), and the double rotation and wagging mode in non-planar pyrocatechin (or pyramidal acetone). The group structures, however, are seen to be the same. The Longuet-Higgins theory yields indeed the same Molecular Symmetry Groups for both pyramidal uid planar systems. As a result, the NRG theory is seen to furnish a more det ulled information about the dynamics of the non-rigid systems. 

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