Planarity as a factor in determining the rate constant and mechanism of acetal hydrolysis

Abstract

Investigations of the hydrolysis of methyl-α-D-altropyranoside (II), methyl-2,6-anhydro-α-D-altropyranoside (I), and methyl-α-D-glucopyranoside (III) have established that ground-state planarity of the C-2, C-1, O, C-5 region of the glycoside attained in (I) does not lower the energy barrier sufficiently to alter the mechanism from an A1 to an S_E2 process (the increase in the rate constant associated with the A1 process for the 2,6-anhydroglycopyranoside is much smaller than that established for the 2-deoxyglycopyranosides).