Matrix Effect on Hydrogen Atom Tunneling:  Comparison between Hydrogen Addition and Abstraction

Abstract

Hydrogen-atom tunneling from and to linear alkenes in organic matrices at 77 K has been studied for elucidating the effect of matrices on the rate of the tunneling. The rate of hydrogen-atom addition to the vinyl carbon of alkenes does not depend on the length of alkyl chains bonded to the vinyl carbon, whereas the rate of hydrogenatom abstraction by methyl radicals from the allylic carbon decreases with increasing length of alkyl chains bonded to the allylic carbon. These effects are explained as due to the resistance of matrices to the change of the C-C-C bond angle of the reacting carbon during the tunneling. For hydrogen-atom abstraction, the resistance causes the increase of the height of the potential barrier between the entrance and the exit of the tunneling channel, whereas the resistance does not cause the retardation of the tunneling to the vinyl carbon since the bond angle scarcely changes during the tunneling.

Acid formation in polymer solids by radiation-induced chain reactions of diphenyliodonium salts

“…However, the G-values are lower than the value in PVA: 18-44. The lower G-values in polyvinyl acetals will be ascribed to difficulty in formation of tertiary radicals in solids (Ichikawa et al 1999;Ichikawa et al 2000).…”