Reversible reactions of cycloalkane solvent holes. 1. Complexation of cis- and trans-decalin{sup {sm_bullet}+} with alcohols

It is shown that solvent holes in cis- and trans-decalin form complexes with aliphatic alcohols that live 1--100 ns, depending on the solute and the solvent temperature. This complexation has near-zero activation energy and occurs with rate constants of (1--1.2) x 10{sup 11} M{sup {minus}1} s{sup {minus}1} in trans-decalin and 3 x 10{sup 10}M{sup {minus}1} s{sup {minus}1} in cis-decalin. The metastable complex decays by proton transfer (for alcohols higher than ethanol); in concentrated solutions a diffusion-controlled reaction of the complex with a second alcohol molecule occurs. While the stability of the complex increases with the carbon number of the alcohol, the standard heat of the complexation decreases in the opposite direction ({Delta}H{degree} changes from {minus}39 kJ/mol for ethanol to {minus}25 kJ/mol for tert-butanol). The decrease in the standard entropy is small ({Delta}S{degree}{sub 298} > {minus}80 J mol{sup {minus}1} K{sup {minus}1}), approaching zero for higher alcohols. The authors argue that this thermochemistry is due to the polaronic nature of the solvent holes.