A density functional theory study of the pyrolysis mechanisms of indole

Becke's three-parameter hybrid density functional method in conjunction wit h Lee-Yang-Parr's correlation functional (B3LYP) was used to investigate th e pyrolysis mechanisms of indole yielding benzyl cyanide and o- and m-tolun itriles. All equilibrium and transition state structures of the proposed re action 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) b asis set. Two hydrogen migration tautomers of indole, seemingly playing no important roles in the pyrolysis due to destruction of aromaticity of the b enzene ring, were predicted to be easily accessible under the experimental conditions and may be important intermediates in the reactions. Two other t ransition states suggested to play important roles in the experimental stud y were not found and may not exist. Instead stepwise processes via hydrogen migration tautomers arriving at the same products are shown likely to be r esponsible for the observed products. IR spectral features of three hydroge n-migration tautomers are predicted to help future experimental identificat ion. (C) 1999 Elsevier Science B.V. All rights reserved.