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

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: $${\mathrm{C}}_3{\mathrm{D}}_6^{+}+{\mathrm{AH}}_2\to {\mathrm{CD}}_3{\mathrm{CDHCD}}_2\mathrm{H}+{\mathrm{A}}^{+}.$$ Rates of this process relative to that of the reference reaction $${\mathrm{C}}_3{\mathrm{D}}_6^{+}+{\mathrm{cyclo-C}}_5{\mathrm{D}}_{10}\to {\mathrm{C}}_3{\mathrm{D}}_8+{\mathrm{C}}_5{\mathrm{D}}_8^{+}$$ 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: $${\mathrm{C}}_3{\mathrm{D}}_6^{+}+{\mathrm{AH}}_2\to {\mathrm{C}}_3{\mathrm{D}}_6\mathrm{H}+{\mathrm{AH}}^{+}.$$ 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.