Intrinsic conformational preferences of and an anomeric-like effect in 1-substituted silacyclohexanes

摘要

A series of ab initio computations have been performed to estimate the CCSD(T) complete basis set limit of the axial/equatorial energy difference for the chair conformation of 1-fluoro, 1-chloro, 1-methyl, 1-hydroxy, and 1-methoxysilacyclohexanes. The equatorial conformation is more stable than the axial by 0.21 kcal mol(-1) for 1-methylsilacyclohexane, while the axial position is more stable for 1-fluoro, 1-chloro, and 1-methoxysilacyclohexane (by 0.09, 0.40, and 0.15 kcal mol(-1), respectively). The axial and equatorial orientations of 1-hydroxysilacyclohexane are nearly electronically isoenergetic (equatorial favored by 0.03 kcal mol(-1)). Zero point vibrational energy corrections have very little effect on the relative energies (less than 0.08 kcal mol(-1)). These results suggest the presence of an interesting stereoelectronic effect, similar to the anomeric effect, in these silacyclohexanes even without an additional heteroatom, like O, in the ring. (c) 2007 Wiley Periodicals, Inc.