Conformational analysis of carbonyl and thiocarbonyl esters: the HC(=X)YXXXCH(CH 3) 2 (X,Y = O or S) internal rotation

Abstract

The YXXXCH(CH 3) 2 internal rotation in the HC(=X)YCH(CH 3) 2, (X,Y = O or S) series of molecules was studied by the ab initio SCF-MO method using 3–21G and 3–21G + d(0.65S) basis sets. Energies and structures of several conformations of these molecules, determined by gradient geometry refinement, are reported and used to assess the effects of oxygen-bysulphur substitution on molecular properties. The nature and relative importance of intramolecular interactions involving both the −CH(CH 3) 2 and the HC(=X)Y (X,Y = O or S) fragments are also discussed.