Component analysis of the X-C-Y anomeric effect (X = O, S; Y = F, OMe, NHMe) by DFT molecular orbital calculations and NBO analysis

CARB 87

Jonathan K. Watts, jonathan.watts@mcgill.ca1, Melissa L. Trapp2, Noham Weinberg3, and B. Mario Pinto, bpinto@sfu.ca2. (1) Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, QC H3A 2K6, Canada, (2) Department of Chemistry, Simon Fraser University, 8888 University Dr, Burnaby, BC V5A 1S6, Canada, (3) Department of Chemistry, University College of the Fraser Valley, Abbotsford, BC V2S 7M8, Canada
Six 2-Y-substituted oxacyclohexane and thiacyclohexane heterocycles (Y = F, OMe, NHMe) were examined using DFT molecular orbital calculations. Natural bond orbital (NBO) analysis of the total energy behaviour yielded the orbital-interaction factors contributing to the conformational equilibria. The dipole moments of the optimized systems were used to estimate the electrostatic contributions to the anomeric effect. The primary determinant of the X-C-Y anomeric effect was found to be the orbital interaction components associated with the combined endo- and exo- anomeric effects acting in concert in the axial conformers. Electrostatic interactions made a contribution to the observed conformer stabilization in all cases, but did not account for the relative magnitudes of the energy differences between conformers of homologous molecules. In the case of the methylamino substituent, accentuated steric interactions in the axial conformer precluded stabilization by the exo-anomeric interaction and consequently, the net endo/exo anomeric stabilization did not dominate the conformational equilibria.
 

General Papers: Analytical Chemistry and Biochemistry of Carbohydrates and Derivatives
8:30 AM-12:30 PM, Thursday, 30 March 2006 Georgia World Congress Center -- B409, Oral

Division of Carbohydrate Chemistry

The 231st ACS National Meeting, Atlanta, GA, March 26-30, 2006