Secondary deuterium kinetic isotope effects in the solvolysis of 4-t-butylcyclohexyl and bicyclo[3.2.1]octan-3-yl toluene-p-sulphonates. New results using 50% aqueous ethanol, acetic acid, and 97% aqueous hexafluoropropan-2-ol

Abstract

Secondary α-deuterium kinetic isotope effects for the solvolysis of cis- and trans-4-t-butylcyclohexyl toluene-p-sulphonates in 50% aqueous ethanol (1.200 ∓ 0.007 and 1.16 ∓ 0.01 respectively, 44.8°), acetic acid (1.172 ∓ 0.004 and 1.13 ∓ 0.01 respectively, 79.6°), and 97% aqueous hexafluoropropan-2-ol (1.232 ∓ 0.013, 40.0° and 1.175 ∓ 0.010, 56.2°, respectively) and for the solvolysis of endo- and exo-bicyclo[3.2.1]octan-3-yl toluene-p-sulphonates in 97% aqueous hexafluoropropan-2-ol (1.246 ∓ 0.009 and 1.234 ∓ 0.004 respectively, 25.2°) have been measured. Mechanisms for these reactions which involve ion-pair intermediates are proposed. Even in 97% aqueous hexafluropropan-2-ol, intimate ion-pairs from trans-4-t-butylcyclohexyl toluene-p-sulphonate undergo further reaction more rapidly than internal return. The other three compounds investigated in this highly ionizing solvent of low nucleophilicity are believed to react, as anticipated, through reversibly formed intimate ion-pairs.