Rotational barriers in 2-dimethylamino-1,3,4-oxadiazoles and -thiadiazoles. A CNDO/2 study

Abstract

The barriers to rotation of the dimethylamino-group in a series of 5-substituted 2-dimethylamino-1,3,4-oxadiazoles and -thiadiazoles have been calculated by the CNDO/2 method with and without d-orbitals in the basis set for sulphur. When a planar dimethylamino-nitrogen atom is employed, the experimental barriers are very satisfactorily reproduced, but when allowance is made for a pyramidal nitrogen atom, quite unrealistic results are obtained. The effects of d-orbitals and of pyramidalisation are analysed and discussed.