Deuterium Isotope Effects for Migrating and Nonmigrating Groups in the Solvolysis of Neopentyl-Type Esters

Article abstract of DOI:10.1021/ja00392a031

α- and γ-deuterium rate effects on the solvolysis of (1-methylcyclohexyl)methyl, (1-methylcyclopentyl)methyl, and (1-methylcyclobutyl)methyl sulfonate esters have been measured and the solvolysis products examined by 2H NMR spectroscopy.The results indicate that the products of the solvolysis of all these sulfonate esters are predominantely ((*) 98percent) rearranged.In the solvolysis of (1-methylcyclohexyl)methyl triflate, rearranged products with methyl migration slightly dominate over those with ring expansion.Normal isotope effects, 1.057 in 80E and 1.073 in 97T, are observed for the methyl-d3 compound and an inverse effect, 0,963, is observed in 80E for the methylene-d4 compound.However, in the solvolysis of both (1-methylcyclopentyl)methyl and (1-methylcyclobutyl)methyl sulfonates, the major products are those of ring expansion.In these examples, inverse effects are observed for the methyl-d3-labeled species.The observed isotope effects can be separated into respective values of 0.927, 0.913 for the nonmigrating methyl-d3 group and 1.177, 1.224 for the migrating methyl-d3 group in the solvolysis of (1-methylcyclohexyl)methyl triflate and (1-methylcyclopentyl)methyl brosylate.This explains the relative intramolecular migratory aptitudes of CH3/CD3 of 1.20 - 1.30 and the low γ-d9 isotope effect in the solvolysis of neopentyl sulfonates previously reported and makes them consistent with a mechanism which involves neighboring carbon participation during ionization.