摘要：

This paper attacks the problem of reducing the activation energy of a Cope rearrangement to a negative number. The molecular orbitals of semibullvalene and the transition state for its Cope rearrangement are constructed. Then the effect of different substituent patterns on the energy of reactant or transition state is evaluated with emphasis on the effect of substituents on the strength of the cyclopropane 2-8 σ bond and on the destabilizing AS transition state orbital. The interesting general conclusion is that in this molecular framework the substituents are as likely to promote or retard a reaction by influencing the stability of reactant or product as they are by influencing the transition state. Specifically strong equilibrium preferences are predicted for π-electron donor or acceptor substituents unsymmetrically substituted, and a lowering or raising of the Cope rearrangement activation energy on appropriate symmetric substitution.

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