Contact ion pairs and solvent-separated ion pairs from D-mannopyranosyl and D-glucopyranosyl triflates.

The chemical nature of contact ion pairs and solvent-separated ion pairs from 2,3,4,6-tetra-O-methyl-α-D-mannopyranosyl triflate was investigated at the DFT(M06-2X) level of theory. Comparison of the present results to those obtained for the D-glucopyranosyl counterpart in our previous study indicated that the ion pairs from the D-mannopyranosyl triflate adopt B2,5-like conformations more preferably than those from the D-glucopyranosyl triflate. Similarly, 1,6-anhydro-D-mannopyranosyl dioxacarbenium ions bearing a (1)C4 conformation were shown to be more stable than the D-glucopyranosyl counterparts.