Abstract
The cation‐radical of 2‐hydroxyoxol‐2‐ene (1^+·^) represents the first lactone enol ion whose structure and gas‐phase ion chemistry have been studied by experiment and theory. Ion 1^+·^ was generated by the McLafferty rearrangement in ionized 2‐acetylbutane‐4‐lactone and characterized by accurate mass measurements, isotope labeling, metastable ion and collisionally activated dissociation (CAD) spectra. Metastable 1^+·^ undergoes competitive losses of H‐4 and CO that show interesting deuterium and ^13^C isotope effects. The elimination of CO from metastable 1^+·^ shows a bimodal distribution of kinetic energy release and produces ^·^CH~2~CH~2~CHOH^+^ (14^+·^) and CH~3~CHCHOH^+·^ (15^+·^) in ratios which are subject to deuterium isotope effects. Ab initio calculations at the G2(MP2) level of theory show that 1^+·^ is 105 kJ mol^−1^ more stable than its oxo form, [butane‐4‐lactone]^+·^(2^+·^). The elimination of CO from 1^+·^ involves multiple isomerizations by hydrogen migrations and proceeds through ion–molecule complexes of CO with 14^+·^ and 15^+·^. In addition, CO is calculated to catalyze an exothermic isomerization 14^+·^ → 15^+·^ in the ion–molecule complexes. Multiple consecutive hydrogen migrations in metastable 1^+·^, as modeled by RRKM calculations on the G2(MP2) potential energy surface, explain the unusual deuterium kinetic isotope effects on the CO elimination. Copyright © 2002 John Wiley & Sons, Ltd.