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

Abstract

Abstract 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. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007