The structure and conformation of bisoxirane and bicyclopropyl

Abstract

Ab initio studies of the molecular conformations of bisoxirane and the isoelectronic molecule bicyclopropyl are reported. All stationary points for both the meso- and d,l-forms of bisoxirane, and bicyclopropyl were optimized at the SCF/6-31G ∗∗ level. Vibrational frequencies were also calculated at the same level. To evaluate the effect of electron correlation on the conformational energies and barriers to internal rotation, single point calculations were performed for all stationary points at the MP4(SDQ)/6-311G ∗∗ level. Based on our calculations, we predict that meso-bisoxirane exists in the gas phase as a mixture of three conformers, a centrosymmetric trans form and a pair of equivalent gauche forms. All these forms have almost the same energy. The isoelectronic molecule bicyclopropyl has a similar potential surface, with one trans and two equivalent gauche forms very close in energy. The most stable form of d, l-bisoxirane which has a gauche orientation of the two oxirane rings, lies about 1 kcal mol −1 below a second conformer with a near trans arrangement.