The Role of Spin-Orbit Coupling and Symmetry in Oxadi-pi-methane Rearrangements and Some Related Photochemical Reactions

The spin-orbit coupling components in the effective one-electron Hamiltonian operator, with the inclusion of symmetry, have been used to formulate mechanisms of spin inversion in triplet reactions for the radiationless decay of triplet complexes to singlet ground state products. This has been applied to investigate the photochemical behavior of oxadi-pi-methane rearrangement in beta,gamma-unsaturated carbonyl cyclic and acyclic systems. It is found that the 1,2-acyl-migrated endo isomer is the most favorable product due to its larger spin-orbit coupling expression as well as better initial overlaps (owing to the less atomic motion). Other related photorearrangements of some molecular systems, such as azadi-pi-methane rearrangement, 4-aryl-substituted cyclopentenones, spirocyclic beta,gamma,delta,epsilon-unsaturated ketones, and heavy atom effect, have also been investigated.