Why 6-methylpentacene deconjugates but avoids the thermally allowed unimolecular mechanism.
[reaction: see text] Tautomeric equilibria involving hydrogen migration in methylacenes were explored computationally using DFT methods. As the aromatic system becomes more extended, the methylene isomer is predicted to become favored. Reasonable-looking pericyclic sigmatropic hydrogen shifts are found to be energetically prohibitive, and bimolecular mechanisms involving radical pair intermediates are energetically feasible.
Norton
Joseph E
JE
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
Northrop
Brian H
BH
Nuckolls
Colin
C
Houk
K N
KN