Wagging band progression

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

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). 

V) The normal modes of the side chains in the all-trans structure can be better identified when the band progressions of the q O "phonons are considered [5-7]. We expect, in principle, to find the well known and characteristic band progressions for the CH2 wagging-twisting (very weak) (1400-1200 cm" ) and CH2 rocking modes (1100-700 cm ) [35]. The band progression of the C-C stretching modes should... 

Fig. 2.11 Infrared spectrum of long-chain [(—CH2)i6—] crystalline stearamide which exhibits band progressions in wagging region.

Figure 2.22. The one-photon LIF excitation spectra of C12CS recorded under (a) cooled (P — 4 atm) and (b) warm (P = 400 Torr) jet conditions. Leaders, denote the progression in quanta of the Q4 out-of-plane wagging mode 0, 2, and 4, refer to the ()[j, 4 , and 4 transitions attached to quanta n of the Q mode, l, —1 and -2, designate the first and second hot band transitions 4 and 4. (Reprinted with permission from Ref. [15].)...

Boolaamphiphiles with two reactive head groups at both ends may bind in a linear or bent fashion to metal surfaces. The only example of a folded bolaamphiphiles on solid surfaces is provided by HOOC—(CH2)3o—COOH on silver. Ellipsometry yielded a surface film thickness of 20 2 A. In the reflection infrared spectra, the 2928 cm shoulder, as well as the lack of sharp bands between 1150 and 1350 cm for the progression of wagging modes indicated that the all-trans sequence length in the surface film should be much less than for the fully extended chain in the KBr pressed disk sample (Figure 6.23) . 

The other experimental data about the out-of-plane displacements comes from the hot band structure in the S 7 S0 absorption that lies in the near ultraviolet region of the spectrum.[5-6] The intensities of the bands in an electronic system depend on Franck-Condon overlap factors that, in turn, depend on the structural differences between the states connected by the electronic transition. The major differences between the S0 and Si states is an out-of-plane distortion of the C=0 group in the upper Sj electronic state. As a result, the spectrum displays long progressions in the wagging normal mode Q)9. At room temperature, the intervals between the hot bands at the red end of the spectrum establish the vibrational intervals in the wagging mode. 

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. 

The progression bands were not only valuable for identification of homologues, but also for distinguishing different crystal forms of fatty acids. The intensity of the wagging progression bands is dependent on the crystal structure. Nujol spectra of the A, B and C forms of two odd-numbered acids (chain length C15, C17) and of the A, B and C forms of one even-numbered acid (Cie) have been published (von Sydow, 1955). The spectral features of the different crystal forms were studied using polarized spectra and variable temperature techniques (Susi and Smith, 1960 Chapman, 1962). 

It should be mentioned that in the expanded region of 1150-1350 cm (Fig. 9), there is a progression of bands, corresponding to the CH2 wagging and indicative of all-trans arrangement of straight hydrocarbon chain (90). This is consistent with the models in Figure 4 proposed from the XRD data. 

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