Non-alternant Hydrocarbon Substituents as Powerful Carbenium-ion Stabilizers: A Graph-theoretical Study with PM3 Support

Abstract

Graph-theoretical arguments establish that some non-fused, even, non-alternant bicycles have unequal numbers of bonding and antibonding orbitals. Both HÜckel and PM3 semiempirical calculations support the contention that such molecules have non-additive π-polarizations relative to the simple π-polarizations of even, non-alternant monocycles. The dicyclopropenyl substituent derived from the corresponding symmetric, contiguous, non-fused, non-alternant bicycle is shown to be a powerful carbocation stabilizer at the PM3 level of theory. Methine cyclopropenyl is shown to be another potent non-alternant carbenium-ion stabilizer.