A Density Functional Theory Study of the Pyrolysis Mechanisms of Indole

Becke\u27s three-parameter hybrid density functional method in conjunction with Lee-Yang-Parr\u27s correlation functional (B3LYP) was used to investigate the pyrolysis mechanisms of indole yielding benzyl cyanide and o- and m- tolunitriles. All equilibrium and transition state structures of the proposed reaction channels were fully optimized by B3LYP using the 6-31G** basis set. Single point energies were evaluated by B3LYP with the 6-311 + + G(2d,2p) basis set. Two hydrogen migration tautomers of indole, seemingly playing no important roles in the pyrolysis due to destruction of aromaticity of the benzene ring, were predicted to be easily accessible under the experimental conditions and may be important intermediates in the reactions. Two other transition states suggested to play important roles in the experimental study were not found and may not exist. Instead stepwise processes via hydrogen migration tautomers arriving at the same products are shown likely to be responsible for the observed products. IR spectral features of three hydrogen-migration tautomers are predicted to help future experimental identification