Reversible Reactions of Cycloalkane Solvent Holes. 2. Scavenging of cis- and trans-Decalin•+ by Benzene

Abstract

Solvent holes in liquid cis- and trans-decalin form metastable complexes with benzene, which are probably solvation complexes of monomer radical cations of benzene. At 25 °C, the rate constants of formation of the complexes are, for trans- and cis-decalin respectively 1.1 × 1011 and 3.6 × 1010 M-1 s-1, and the natural lifetime of the complex is 7 ns for trans- and 50 ns for cis-decalin. Thermodynamic potentials for the complexation are determined. The heat of the complex formation is ≈−26 kJ/mol for trans- and ≈−18 kJ/mol for cis-decalin. In cis-decalin, the complexes are more stable because of near-zero entropy of the complex formation. The complex decays by proton or H atom transfer with activation energy ≈10 kJ/mol (which yields a benzonium cation) or in a reactive encounter with a second benzene molecule (which yields a benzene dimer cation). Laser excitation of the dimer cation with a 1.165- or 2.33 eV photon causes valence band electron transfer and injection of a free solvent hole.