Reactions of CH3CHO·+ and of CH3COH·+ with water upon Fourier transform ion cyclotron resonance conditions

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Eur. J. Mass Spectrom. 9, 319 - 326 (2003)
DOI: 10.1255/ejms.564

Reactions of CH₃CHO^·+ and of CH₃COH^·+ with water upon Fourier transform ion cyclotron resonance conditions

H. Nedev, G. van der Rest, P. Mourgues^* and H.E. Audier
Laboratoire des Mécanismes Réactionnels, UMR CNRS, Ecole Polytechnique, F-91128, Palaiseau, France. E-mail:

ABSTRACT:

The reactions of CH₃CHO^·+ and of CH₃COH^·+ with water yield the same products, at almost the same rate. It is shown, by using a characteristic reaction of the carbene structure, that a molecule of water converts CH₃COH^·+ into its more stable isomer CH₃CHO^·+, which is a new example of catalyzed 1,2-H transfer. The dominant product is the proton-bound dimer of water which, in fact, comes from the [H₂OH⁺...CH₃^·] and [H₂OH⁺...CO] primary products whose observed abundances are poor. In a related system, ionized formamide/water, a water molecule catalyzes the 1,3-transfer leading from the solvated carbene to the [H₂O...H⁺...H₂NC=O^·] stable intermediate, which eliminates CO without back energy. In contrast, such a process does not take place in the studied system since the cleavage of the so formed [H₂OH⁺...CH₃CO^·] transient intermediate involves a high back energy; this is explained by the charge repartition within this intermediate. In fact, a different pathway takes place. The solvated acetaldehyde ion isomerizes into a terbody intermediate in which protonated water is bonded to a CO molecule on the one hand and to a methyl radical on the other hand. Simple cleavages of this complex yield the observed products.

Keywords: catalyzed isomerization, ionized carbenes, FT-ICR mass spectrometry, ab initio calculations

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