J. Chem. Soc., Perkin Trans. 2, 1999, 1059 - 1062, DOI: 10.1039/a902279a
Spin isomerisation of para-substituted phenyl cations
Massimiliano Aschi and Jeremy N. Harvey
The singlet and triplet potential energy surfaces of a series of p-X-substituted
aryl cations (X = H, CN, CH3, F, OH, NH2)
are investigated computationally at the B3LYP/6-31G(d) level of theory. The
first four species are found to be ground state singlets, the last has a triplet
ground state, and the spin states of the OH derivative are almost isoenergetic.
The minimum energy crossing points (MECPs) between the two surfaces are found to
lie very little above the higher of the two minima in all cases, and the
spin-orbit coupling is significant at those points. Therefore, it is expected
that aryl cations will rapidly convert to their most stable spin state, and that
in cases of near degeneracy such as for p-HO-C6H4+,
the states may interconvert rapidly enough to both be accessible in thermal
reactions.