Is. Ignatyev et T. Sundius, Competitive ring hydride shifts and tolyl-benzyl rearrangements in tolyl and silatolyl cations, CHEM P LETT, 326(1-2), 2000, pp. 101-108
Transition states for two plausible isomerization pathways of tolyl and sil
atolyl cations are predicted at the wB3LYP/6-31(d,p) level of theory. The b
arrier heights for the interconversion of the ortho- and meta-isomers are h
igh for both tolyl (50 kcal/mol) and silatolyl (57 kcal/mol) cations. Compe
titive hydride shifts from methyl and silyl groups to the positive charge c
enter at the phenyl ring leading to benzyl and silabenzyl cations have suff
iciently different barrier heights: the one for tolyl cation (26 kcal/mol)
is close to the upper excess energy limit of the nucleogenic tolyl cation,
while this barrier for the silatolyl cation is substantially lower (9 kcal/
mol). Stationary points for the path leading from the benzyl cation to the
global minimum of the C7H7+ system, i.e. the tropylium cation, were also fo
und. (C) 2000 Published by Elsevier Science B.V.