Steady state and laser flash photolysis of acenaphthenequinone in the presence of olefins

Abstract

The rate constants for the quenching of acenaphthenequinone triplet by olefins, in degassed benzene solution, have been measured by laser flash photolysis. The alkenes studied included acyclic, cyclic, isolated and conjugated dienes, and vinyl ethers. The quenching rate constant ranges from 2.1 × 10⁶ M^–1 s^–1 for hexa-1,5-diene to 6.0 × 10⁸ M^–1 s^–1 for 2,3-dimethylbut-2-ene. A plot of log k_qversus the ionization potential for some of the olefins employed is linear (r = 0.89), with a slope of –1.5/eV. The magnitude of this slope, as well as the inverse solvent effect found in the quenching process, i.e.k_q(ACN)/k_q(benzene) = 0.3–0.5, are consistent with a mechanism involving a partial charge transfer complex. Steady state photolysis of acenaphthenequinone in the presence of cyclohexene, 2-methylbut-1-ene, 2-methylbut-2-ene, trans-penta-1,3-diene, cis-penta-1,3-diene, trans-stilbene, cis-stilbene, ethyl vinyl ether, and 2,5-dimethylhexa-2,4-diene led only to products resulting from a photocycloaddition process.