PROTON-TRANSFER REACTIONS IN THE SIMPLE ALKANES: METHANE, ETHANE, PROPANE, BUTANE, PENTANE, AND HEXANE.

Proton‐transfer reactions from CHO+ and CDO+ to the simple alkanes, methane through hexane, have been investigated in a tandem mass spectrometer. Acetaldehyde is shown to be the molecular source yielding CHO+ reactant with the lowest internal excitation energy. The translational energy dependence observed for the reactions CHO++CH4→CX5++CO, CX5+→CX3++X2 (X=H or D) suggests that the interaction is better represented over the energy range considered as proton stripping rather than as proceeding through an intermediate [CXO+–CX4]* complex. In addition, there is no evidence from isotope effects for a transition in mechanism. A highly simplified model treating the protonated methane species as a collection of closely coupled harmonic oscillators permits application of the classic rate expression for unimolecular decomposition to the dissociation yielding CH3+, and this relation provides a reasonable semiempirical fit to the experimental data. The reaction of CHO+ with ethane at quasithermal energy yields C2H7+...