Abstract

European Journal of Mass Spectrometry
Volume 10 Issue 6, Pages 775–782 (2004)
doi: 10.1255/ejms.707

The formation and heats of formation of simple α-distonic ions

Lars Bo Jensen and Steen Hammerum
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark

Several methods for the preparation of α-distonic radical cations by unimolecular fragmentation in the gas phase have been examined, but generally applicable and satisfactory methods were not found. One commonly encountered problem is the contamination of the product ion beam by isotopic contributions from ions whose nominal mass is one unit lower (often formed by simple cleavage of the precursor ion). A novel α-distonic ion, (CH₃)₂NHCH₂⁺·, was discovered and characterized. Composite ab initio methods of the G3 and CBS families were used to determine the heats of formation of the molecular ions and the α-distonic isomers of simple alcohols, ethers and amines with up to four carbon atoms. The α-distonic isomers are the lower energy species only for ionized alcohols and primary amines.

Keywords: radical cations, ab initio calculations, unimolecular reactions, ionized methylacetamides, α-distonic ions, extrusion reactions, reaction mechanism

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