¹³C NMR study of some derivatives of 1,3,4‐oxadiazoles, 1,3,4‐thiadiazoles and isosydnones

Abstract

Abstract The assignment of all ring carbons of 37 derivatives of 1,3,4‐oxa‐ or thiadiazoles and of seven isosydnones is described. In some cases, 13 C‐labelled compounds were used. The analysis of substituent effects and the calculation of charge densities of some of the derivatives suggest that the two nitrogen atoms form a protective screen against electron perturbation and play the role of an ‘electronic buffer’. A notable variation of chemical shifts could be observed only when oxygen is replaced by sulphur.