Azolides. Part 12. Carbon-13 nuclear magnetic resonance study of N-methyl and N-acetyl derivatives of azoles and benzazoles

Abstract

13 C N.m.r. chemical shifts and C–H coupling constants of methyl- and acetyl-benzazoles have been derived from data for the corresponding uncondensed azoles by addition of increments which depend on the position and nature of the azole nitrogen atoms present. Use of 13C n.m.r. parameters by estimation of conformer distribution in acetylazoles or -benzazoles proved reliable only when the individual conformers were observable. In the absence of steric effects the composition of equilibrium mixtures of isomeric N-substituted azoles is independent of the nature of the N-substituent.