Thermal ion–molecule reactions in oxygen-containing molecules. Inverse isotope effect in the ion–molecule dimerization reactions of protonated propyl acetate ions

Abstract

Thermal ion–molecule dimerization reactions of protonated molecular ions in [²H₃]n- and [²H₃]iso-propylacetate have been studied with a time-of-flight mass spectrometer. CD₃COOH⁺₂ and CD₃CO⁺ ions react with the neutral molecules to form CD₃COOC₃H₇H⁺ and CD₃COOC₃H₇D⁺ ions. These CD₃COOC₃H₇H⁺ and CD₃COOC₃H₇D⁺ ions subsequently react with the neutral molecules to form (CD₃COOC₃H₇)₂D⁺ ions by bimolecular dimerization reactions in which an inverse isotope effect is observed. The effect of various reaction conditions on the isotope effect has been studied and the relation between the isotope effect and the dimerization reaction mechanism is discussed.