EFFECT OF BENZANNELATION ON THE CONFORMATIONAL FLEXIBILITY OF THE RINGS IN OXO, IMINO, AND METHYLENE DERIVATIVES OF CYCLOHEXA-1,4-DIENE

The effect of benzannelation on the equilibrium conformation and flexi bility of the dihydrocycle in cydohexa-1,4-dienone, para-quinone, and their imino and methylene analogs was studied by the semiempirical qua ntum-chemical AM1 method. The equilibrium conformations of the carbony l derivatives are planar. In the imino- and methylene-substituted anal ogs, the dihydrocycle adopts a boat conformation due to repulsions bet ween the hydrogen atoms at the exocyclic double bond acid in the peri positions of the benzene rings. Annelation of cyclohexa-2,5-dien-1-one and para-quinone with benzene rings at the C=C double bonds causes an increase in the conformational flexibility of the partially hydrogena ted ring owing to an increase in the bending strain in the first compo und and a decrease in the conjugation between the carbonyl groups and the remaining pan of the molecule in the second compound.