Reactions of Triplet Diphenylcarbene by Hydrogen Atom Tunneling in Rigid Media

Article abstract of DOI:10.1021/ja00388a003

Photolysis of diphenyldiazomethane in six matrices (toluene, methylcyclohexane, benzene, diethyl ether, 2-propanol, and cyclohexene) and their deuterated modifications at low temperature gave rise to the metastable triplet ESR spectrum of diphenylcarbene.Chemical and kinetic isotope effects established that the mechanism of the signal decay was hydrogen atom abstraction by the triplet ground state of diphenylcarbene from the matrix host.Analysis of the decay kinetics revealed that this process occurs by quantum mechanical tunneling of the hyfrogen atom.Calculations based upon an Eckart barrier potential reproduced the experimental rate constants faithfully and gave reasonable values for the barrier width and height parameters.It was found that the signal decay in proton and perdeuterated matrices corresponded to sites of very different reactivity.The implications of the tunnel effect for the chemistry observed in low-temperature matrices are discussed.