Ab Initio Theoretical Studies on the Ring-Opening Modes of the Oxiranyl-, Aziridinyl-, Oxaziridinyl-, and Thiaranylmethyl Radical Systems

Abstract

Ab initio theoretical studies have been carried out on the oxiranyl-, aziridinyl-, oxaziridinyl-, and thiaranylmethyl radical systems and on the various possible conformations of the ring-opened heteroallyllic radical systems derived by ring opening of the first three systems. Previous theoretical studies on the ring opening of the oxiranylmethyl radical indicated that there is an overwhelming thermodynamic preference for the formation of the allyloxy radical over the formation of the (vinyloxy)methyl radical. The results of the present theoretical studies on the potential energy surfaces for ring opening also indicate a strong kinetic preference for allyloxy radical formation over the formation of the (vinyloxy)methyl radical. The results of the present calculations on the aziridinylmethyl radical indicates that it kinetically prefers to ring open by cleavage of the C−N bond, but thermodynamically by cleavage of the C−C bond. The results of the calculations on the C2H4NO radical system indicate that ring opening of the oxaziridinylmethyl radical by C−O bond cleavage is both thermodynamically and kinetically favored over C−N bond cleavage. Calculations on the thiaranylmethyl radical suggest that it does not represent a minimum-energy structure on the C3H5S potential energy surface.