The haloacetyl ions; a thermochemical study

The haloacetyl ions XCH₂CO⁺], X = Cl, Br, I, have been produced by the dissociative ionization of selected precursor molecules and identified via their fragmentation characteristics. Their heats of formation, Δ, were 708 ± 8, 750 ± 25 and 784 ± 10 kJ mol^?1, respectively, all appreciably above ΔH for CH₃CO⁺], 653 kJ mol^?1. The effect of halogen substitution α to carbonyl is discussed for neutral molecules and their molecular ions.