The Unimolecular Dissociation of (CH3)2C⊕CH2COOH in the Gas Phase: An Acid-Ester Type Rearrangement Involving the Formation of the Proton-Bound Acetone-Ketene Ion [(CH3)2C=O⋯H⋯CH2=C=O]⊕

Abstract

In the gas phase the β-ketocarbenium ion (CH₃)₂C^⊕CH₂COOH is proposed to rearrange to the proton-bound acetone-ketene ion [(CH₃)₂CO⋯H⋯CH₂CO]^⊕, prior to its dissociation into CH₃CO^⊕/(CH₃)₂CO and (CH₃)₂COH^⊕/CH₂CO. Collision experiments in a mass spectrometer of reversed geometry on ²H- and ¹³C-labeled isotopomers indicate that this remarkable rearrangement is characterized by two consecutive [1,5]-proton migrations rather than a direct [1,3]-hydrogen shift.