Structures of cyclic amides. Part III. Thio- and seleno-lactams

Abstract

A comprehensive concentration study has been made of the ν(N–H) stretching frequencies of the thio- and selenolactams, [[graphic omitted]H (n = 3–11). The results are compared with the oxylactams and are discussed in terms of cis-, trans-, and skew-conformations of the peptide link. The transition cis→trans occurs at n= 7 and in this compound four different monomeric conformations are shown to co-exist. I.r. criteria are presented for cis- and trans-conformations of the thio- and seleno-peptide link in cyclic systems.

The association characteristics of these conformations are reported and criteria presented for cis- and trans- association.