Gas-Phase Radiolysis of Cyclopentane. Relative Rates of H2−-Transfer Reactions from Various Hydrocarbons to C3H6+

Abstract

The radiolysis of cyclo-C5D10 has been investigated in the presence of various saturated and unsaturated perprotonated hydrocarbons. On the basis of the isotopic analysis of the propanes formed in these mixtures and several other experimental observations it is concluded that the C3D6+ ion, which is the major ion produced in the fragmentation of C5D10+, reacts with various saturated hydrocarbons (AH2) as follows: C3D6++AH2→CD3CDHCD2H+A+.Rates of this process relative to that of the reference reactionC3D6++cyclo−C5D10→C3D8+C5D8+have been measured with an accuracy of better than 2%. It is suggested that the saturated hydrocarbons also transfer an H− ion to C3D6+ according to the following reaction: C3D6++AH2→C3D6H+AH+.Although in agreement with theory the total rate of reaction of C3D6+ with AH2 is generally seen to increase with an increase in molecular weight of AH2, there are appreciable variations in the rates of the H2− transfer reaction (a) versus that of the H−-transfer reaction (c) with a change in structure of the hydrocarbon molecule. Reaction (c) is usually favored when AH2 is a branched hydrocarbon, except for neopentane which is entirely unreactive toward C3D6+. Unsaturated hydrocarbons do not transfer an H2− ion to C3D6+ but probably undergo a condensation-type process. The radiolysis of cyclopentane has also been investigated in the presence of O2, NO, and (CH3)3N. It is demonstrated that the C3H6+ and C5H10+ ions transfer their charge to NO, or (CH3)3N and that at a pressure of 20 torr approximately 20% of the parent ions undergo ring opening prior to the charge-transfer process.