Gas-phase Unimolecular Reactivity of C3H7O+ Cations: a Combined Mass Spectrometric-Molecular Orbital Study

Abstract

The unimolecular dissociations of the two isomeric ions [CH3CH2CHOH]+ (1) and [CH3CH2OCH2]+ (2) were re-examined. Molecular orbital calculations conducted at the MP2/6–31G*//HF/6–31G*+ZPE level were used to characterize the corresponding potential energy profile. The experimental data were completed by a Fourier transform ion cyclotron resonance spectrometric investigation on the system [CH2OH]++C2H4 and by a study of various metastable [C3H7O]+ ions. The isomerization pathway of lowest energy connecting 1 and 2 involves two ion–neutral complexes between protonated formaldehyde and ethene. The isomerization 1 - 2 is typically a complex mediated reaction since the key step consists simply of the reorientation of the two partners [CH2OH]+ and C2H4 inside the ion–neutral cage. The model is demonstrated to account for the H–D exchange observed during the dissociation of variously deuterated species. © 1997 by John Wiley & Sons, Ltd.