Vibrational spectra vinyl group

Figure 9.49 shows the SVLF spectrum of styrene (C6H5CH=CH2), in a supersonic jet, with excitation in the ()[j band of the A1 A — X] A (6) — S0) band system. There is a prominent progression in the vibration v42 which is a torsional motion of the vinyl group about the C(l)-C(a) bond. The vibronic selection rules allow only transitions with Av42 even. Those with V42 = 0, 2, 4, 6 and 10 are observed. More vibrational levels, with V42 even and odd, have been identified and fitted to a torsional potential function of the type in Equation (6.96) giving... 

The i.r. and Raman spectra of trivinylborane, B(CH=CH2)3, may be assigned on the basis of the planar, C3h, structure determined by electron diffraction. The values of v(B—C) and v(C=C) are consistent with some B—C 7r-interaction.141 A second, independent, investigation of this vibrational spectrum agrees with these conclusions for the solid phase, but in the fluid phases an additional conformer, of Cs symmetry, was detected.142 This form may be obtained by twisting the vinyl groups out of the molecular olane. 

The Raman spectrum of PS shows a couple of distinctive doublets at 1603 and 1584 cm and at 1033 and 1002 cm , both ring-mode vibrations, and both characteristic of a monosubstituted aromatic compound. The Raman band at 622 cm is also indicative of the substituted benzene ring. In addition, there are a few IR absorption peaks due to functional groups such as terminal vinyl group at 907 and 980 cm (refer to 910 and 990 cm peaks of PE) and the irons C=C double bond at 967 cm" resulting from termination reactions. Note also that these bands can also be assigned to trace amounts of butadiene that are sometimes added to polystyrene when it is used for making thin films. This addition adds some flexibility and reduces the brittle nature of the polystyrene film. Atactic polystyrene has bands related to its atactic nature at 1370, 1328, 1306, 1070, and 943 cm and the isotactic form exhibits bands at [62] 1364, 1314, 1297 cm and a doublet at 1075 and 1056 cm (see Fig. 32). As isotactic polystyrene crystallizes, the doublet is seen to shift to 1080 and 1048 cm, and a new band appears at 985 cm The crystallinity may be determined from the intensity of the 985 cm band, and the ratio 566/ 543 is used to evaluate the content of isotactic sequence. For refer-... 

The vinyl group in polybutadienes has been studied more extensively than simple alkenes, and it has a similar spectrum with peaks at about 4484, 4597, and 4660 cm" Bands at 4717 and 4481 cm in polybutadiene have been assigned as second overtones of the symmetric and asymmetric bending vibrations of the CH2 of the uncoupled vinyl group, as interpreted by a local mode model. There are no corresponding fundamental vibrations for these peaks at 1469 and 1572 cm" though ... 

In the first case, this polymerization route yields a terminal vinyl group, so a pair of strong bands characteristic of the vinyl group would be expected to be observed near 990 and 905 cm and they are clearly present. The second reaction path should yield either or both cis and trans polymers, and for these structures bands should be found near 700 cm ( 40 cm, w and b, cis) and 965 cm ( 5 cm vs, trans), respectively. The rest of the polybutadiene spectrum would be expected to exhibit the C=C stretching modes near 1650 cm (the band is split by the cis and vinyl modes, the trans mode is very weak and hard to identify) and C—H stretching vibrations for both sp -and 5 -hybridized carbon atoms respectively just below and just above 3000 cm The sp band is not well resolved, and it is usually observed as a high-wavenumber shoulder on the sp band (the vinyl CH2 shows near 3100 cm with the rest of the unsaturated C H stretch near 3010 cm ). 

Figure 1 illustrates the IR spectra of NBR and HNBR samples with different concentrations of residual double bonds [11]. The CN stretching vibration is observed at 2222 cm in NBR and HNBR. The peak at 1440 cm is for C—H deformation of —CH2— groups. The =C—H out of plane deformations of trans, vinyl, and cis double bonds are observed at 970 cm", 920 cm", and 730 cm", respectively. These peak absorbances decrease gradually, and a new peak at 723 cm" appears on the spectrum of HNBR for—CH2— rocking vibration [when (CH2)n n > 4] [11,78]. The CN stretching vibration is taken as an internal standard and the... 

The saponification step is accompanied by the disappearance of the photoline of the C=0 carbon of the acetate group at a binding energy of 282.2 eV in the XPS spectrum. In addition, in the IR-ATR spectrum a broad OH stretching vibration band appears at 3410 cm (Fig. 23). According to Clark and Briggs, on subsequent SO2 plasma treatment, sulfate groups are formed [124,125]. SO functions may be incorporated into the poly(vinyl chloride) sequences as well. 

The IR and Raman spectra of polyvinyl acetate are provided in Reference Spectrum 10. Key features of the IR spectrum of PVAc are the C=0 stretching vibration at 1740 cm , the C—O stretching vibration of the ester group at 1230 and 1020 cm , an absorption due to methyl CH bending at 1375 cm , and CH2 bending (scissors) vibration of the methylene groups at 1440 cm . An important copolymer of vinyl acetate is ethylene-vinyl acetate copolymer, EVA. For this copolymer, an increase in the number of —CH2— groups, due to the insertion of ethylene molecules into the polymer... 

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