Benzene second overtone

In addition to the two methyl peaks near 5790 and 5735 cm, the methyl group in aromatic compounds has a band near 5660 cm, which has been found useful for quantitative analysis. Luty and Rohleder assigned this peak to be due to -i- 26. They also suggest that a peak at 4080 cm" is due to 38s, second overtone of a symmetric bending vibration of the CHj group. This peak is well isolated in compounds having multiple methyl groups such as penta and hexa-methyl benzene. 

With regard to higher vibrational states, the second overtone of the aromatic C-H stretch in alkylated benzenes occurs at 8734 cm (1145 nm), whereas the alkyl C-H stretch occurs at 8389 cm" (1192 nm). Approximately 5- to 10-nm shifts were observed to lower frequency (longer wavelength) as compared with benzene s second CH overtone band. 

The model in figure 4.14 results from a 2 1 bend-stretch Fermi resonance model for IVR from benzene overtone states (Sibert et al., 1984a). The first tier is a group of states for which one quantum of CH stretch, Wch. has been transferred to two quanta of CH bend, n. In the second tier an additional cn quantum has been transferred to two more quanta. Though this model is based on strong physical arguments, it is still not known whether this Fermi resonance and tier model is the complete picture for IVR in benzene. 

Deuterated benzene (CgDg) has bands at 1900, 1560,1375, and 1010 nm, which correspond to the first, second, third, and fourth overtones of C-D stretching, respectively." ... 

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