RESUMO
Interaction path analyses for pi-conjugated organic systems were performed at the ab initio molecular orbital level to examine the relationship between inter-radical interactions and the high-spin stability of the system. It was found that the high-spin stability results from through-bond interactions between radicals, not from through-space interactions, in relation to the stabilization of a low-spin state due to the effects of electron correlation. L(ij)(min) value for estimating the mixing of nonbonding molecular orbitals well predicted the relationship between the through-bond interactions and the high-spin stability. Furthermore, molecular orbital calculations revealed that the all-trans type interaction path between radicals produces long-range exchange interactions, and the additivity of high-spin stability is observed by keeping short-range through-bond interaction paths.
RESUMO
Ab initio through-space/bond interaction analysis was applied to [3 + 2] annulation based on Brook rearrangement using beta-phenylthio-acryloylsilanes with alkyl methyl ketone enolates. An uncertain reaction mechanism, wherein a bulky cyclopentenol with large substituents on the same side of the five-membered ring was obtained as a major product, can be explained by the low activation energy of its reaction pathway. Intramolecular orbital interactions related to the carbanion generated by Brook rearrangement preferentially provide the stabilization of the reaction pathway to the bulky cyclopentenol (major product) compared with that provided to the non-bulky cyclopentenol (minor product). In addition, ab initio molecular orbital calculations suggest the existence of an E/Z conformational inversion after Brook rearrangement. This result accurately explains the loss of the E/Z stereochemical integrity in the starting materials of the experiment.
