Internal Rotation of the Methyl Group in the Electronically Excited State: o- and m-Toluidine

Author:

Okuyama Katsuhiko1,Mikami Naohiko1,Ito Mitsuo1

Affiliation:

1. Department of Chemistry, Faculty of Science, Tohoku University, Sendai 980, Japan

Abstract

The fluorescence excitation and dispersed fluorescence spectra of jet-cooled o- and m-toluidine were observed. Vibrational analysis of the spectra provided us with the potentials for the internal rotation of the CH3 group in both ground and excited states. In o-toluidine, a large potential barrier to the internal rotation in the ground state is practically removed in the excited state. On the other hand, a nearly free internal rotation of the CH3 group in the ground state of m-toluidine gains a large barrier by the electronic excitation. The great change in the barrier height upon the electronic excitation is more remarkable than that found for fluorotoluene. A close relationship between the barrier height and the π electron density at the ring carbon atom was found, indicating the hyperconjugation as the origin of the barrier height in the absence of steric hindrance.

Publisher

Hindawi Limited

Subject

Spectroscopy,Biochemistry,Atomic and Molecular Physics, and Optics

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