Reversible reactions of cycloalkane solvent holes. 1. Complexation of cis-and trans-decalin(center dot+) with alcohols

It is shown that solvent holes in cis- and trans-decalin form complexes wit h aliphatic alcohols that live 1-100 ns, depending on the solute and the so lvent temperature. This complexation has near-zero activation energy and oc curs with rate constants of (1-1.2) x 10(11) M-1 s(-1) in trans-decalin and 3 x 10(10) M-1 s(-1) in cis-decalin. The metastable complex decays by prot on transfer (for alcohols higher than ethanol); in concentrated solutions a diffusion-controlled reaction of the complex with a second alcohol molecul e occurs. While the stability of the complex increases with the carbon numb er of the alcohol, the standard heat of the complexation decreases in the o pposite direction (Delta H degrees changes from -39 kJ/mol for ethanol to - 25 kJ/mol for tert-butanol). The decrease in the standard entropy is small (Delta S degrees(298) > -80 J mol(-1) K-1), approaching zero for higher alc ohols. We argue that this thermochemistry is due to the polaronic nature of the solvent holes.