Bending vibrations unsaturated

Table 3.3 Out-of-plane bending vibrations of the C-H bonds in unsaturated groups...

The 1600-1000 cnf region corresponds to the bending vibrations of C-H bonds in unsaturated systems, and can often be used to determine the substitution pattern of aromatic rings. 

The region 667-10 cm" contains the bending vibrations of carbon, nitrogen, oxygen and fluorine with atoms heavier than mass 19, and additional bending motions in cyclic or unsaturated systems. The low-frequency molecular vibrations in the far-infrared are particularly sensitive to changes in the overall structure of the molecule thus the far-infrared bands often differ in a predictable manner for different isomeric forms of the same basic compound. 

Figure 4 illustrates the infrared spectrum for a sample of PPE. The absorptions of the peaks at 3.4, 6.9 and 7.3 pm were assigned to C-H stretch and C-H bending frequencies in CH2 and CH3 (33). These absorptions are proportional to the surface density of deposited ethane (16). However, the absorptions at photons near 10 pm are attributable to OH deformations and CO stretchings of alcoholic groups and vibrations of alkyl ketones (22). They also indicate the existence of branches in unsaturated chain (33). 

Vibrations of triple and cumulative bonds Vibrations of C=X Fingerprint region Unsaturated C-H bending... 

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