MOLECULAR-STRUCTURE AND CONFORMATION FLEXIBILITY OF 2-OXO-1,2,3,4-TETRAHYDROPYRIMIDINE AND 2-THIOXO-1,2,3,4-TETRAHYDROPYRIMIDINES AND THEIRDERIVATIVES

The conformational flexibility and effects of the substituents in 2-ox o- and 2-thioxo-1,2,3,4-tetrahydropyrimidines were studied by the semi empirical quantum-chemical AM1 method. The substituents at the double bond have no appreciable effect on the conformational characteristics of the heterocycle. The introduction of substituents to the saturated carbon atom results in the conversion of the tetrahydrocycle to a half -chair conformation and in a substantial decrease in the ring flexibil ity. The results of calculations are confirmed by the X-ray study of b oth compounds.