ABINITIO COMPUTATIONAL STUDY OF METHANO-BRIDGED AND ETHANO-BRIDGED DERIVATIVES OF OXYALLYL

Ab initio SCF-CI computations on methano-bridged oxyallyl (OA) (3) and ethano-bridged OA (4) indicate that the OA's are ground-state singlet species, with strong C=0 bonds and pronounced diradicaloid character in the Cl wave functions. The computational excited 3B2 π-π⋆ states of 3 and 4 are ~4-7 kcal/mol higher in energy than the 1A1 ground-state diradicaloids. The bicyclobutanone analogue of 3S (5) is predicted to be substantially lower in energy than any of the diradicaloid forms, but the bicyclopentanone analogue of 4S (6) is somewhat higher in energy than 4S. Experimental observation of the triplet manifold of these OA derivatives is likely to be rendered quite difficult by their small singlet-triplet gaps and the thermodynamic accessibility of the bicyclic analogues. Qualitative molecular orbital considerations suggest that electron-rich olefins might be trapped by a nonconcerted mechanism, in accord with recent experimental results. © 1990, American Chemical Society. All rights reserved.