Solvolysis of 1-(3-noradamantyl)ethyl sulfonates

Abstract

The title esters solvolyze in aqueous ethanol (a) almost entirely to the rearranged substitution products 2- methyl-1-adamantyl alcohol and ether, (b) about 1000 times faster than unstrained analogues, (c) by a non-first-order rate law, (d) without oxygen scrambling, and (e) with production of large proportions of the rearranged tertiary 2-methyl-1-adamantyl sulfonate esters as reactive intermediates. The tertiary esters solvolyze (a) to arranged substitution products, (b) 2-7 times faster than the noradamantyl isomers, (c) in clean first-order reactions, and (d) with oxygen scrambling. The formation of rearranged tertiary esters as reactive intermediates in the solvolyses of the secondary esters and the oxygen scrambling during solvolysis of the tertiary esters both show that the solvolyses of the tertiary esters involve large proportions of internal return and are therefore not 'k, processes. In addition, solvent effects on the partitioning of the tertiary ester's tight ion pair between covalent substrate and products are significant and lead to a Grunwald-Winstein m value for internal return that is about 0.5 less than that for solvent separation; this result provides an explanation for the larger-than-average m values observed for 1-adamantyl systems. The &d3 rate effects for solvolysis of the 1-(3-noradamantyl)ethyl esters are in the narrow range of 1.14-1.15, smaller than the value of 01.20 shown by 3,3-dimethyl-2-butyl sulfonates and indicative of carbon a-participation and strong carbon hyperconjugation. Thus, the accelerated solvolysis rates, the absence of internal return, and the lowered isotope effects clearly establish this solvolysis as a kA process. Plots of log k values vs YoT, for the title esters give slopes (m values) around 0.7, while the m values for the adamantyl isomers are around 1. The differences between these plots for structurally very similar reactants solvolyzing with clearly different rate-determining steps are not large and indicate the hazards in using rate correlations to establish solvolytic reaction mechanisms, especially when comparing reactants with greater structural differences. The higher homologues, 1-(3-noradamantyl)propyl sulfonate esters, were found to behave similarly.