Studies on lactams. Part IV. Relation between Cotton effect and conformation of a seven-membered lactam ring

Abstract

The n–π* Cotton effects of seven-membered lactams have been investigated; from the results seven-membered lactams have been classified into two types: A having a negative and B a positive Cotton effect. The derived ‘lactam rule’ has been applied to conformational studies on N-methyl-A-aza-A-homo-tetrahydro-α-santonins and comparisons have been made with N-methyl-(–)-menthone lactam. The conformational equilibrium of a fused seven-membered lactam ring is discussed in the light of c.d. data.