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Electronic spectra of o-, m- and p-tolunitrile—substituent effect on internal rotation of the methyl group

✍ Scribed by Masaaki Fujii; Masayo Yamauchi; Ken Takazawa; Mitsuo Ito

Publisher
Elsevier Science
Year
1994
Tongue
English
Weight
838 KB
Volume
50
Category
Article
ISSN
1386-1425

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✦ Synopsis

The S, +-So fluorescence excitation spectra and the S ,+& dispersed fluorescence spectra of o-, mandp-tolunitrile were measured in supersonic jets. Low-frequency bands due to internal rotation of the methyl group were observed in m-and p-tolunitrile. Observed band positions and relative intensities of the internal rotational bands were reproduced by a calculation using a free rotor basis set. From the analysis, the potential curve of the internal rotation was determined in both S, and St,. It was found that the barrier height increases in going from So to S, in m-tolunitrile, while it decreases in p-tolunitrile. In contrast, no low-frequency band was found in o-tolunitrile. It is concluded that the potential curve in o-tolunitrile does not change in going from S,, to S,. The change of the barrier height by electronic excitation in tolunitriles differs greatly from that observed in other toluene derivatives. It is suggested that the electronic properties of a substituent are important for the methyl rotation in the excited state.

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