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.