Thermal ion–molecule reactions in oxygen-containing molecules. Proton and hydride ion transfer reactions in acetaldehyde

Abstract

The proton and hydride ion transfer reactions in acetaldehyde have been studied on a modified time-of-flight mass spectrometer. The appearance potentials and the ionization efficiency curves of fragment and product ions were measured by the r.p.d. technique and the precursors of the product ions were determined from an analysis of the shapes of these curves. Rate constants for the formation reactions of CH₃CHOH⁺ and CH₃CO⁺ were obtained. The positions from which proton and/or hydrogen atom transfer occur were clarified using [²H₃]2,2,2-acetaldehyde. The rate constant of proton and/or hydrogen atom transfer from the formyl group is larger than that from the methyl group by a factor of two. It was also confirmed that CH⁺₃ abstracts only the hydrogen of the formyl group in the hydride ion transfer reaction. The hydride ion transfer involving CH⁺₃ from methane was studied in acetaldehyde + methane mixtures and its rate constant is larger than that in pure acetaldehyde.