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The bimolecular reaction of the CH2CHOH+ enol ion (m/z 44) with acetaldehyde gives a strongly dominant product, m/z 45, formed mainly by proton transfer from the ion to the molecule. The abundance of the product coming from a H* abstraction reaction from the neutral, albeit more exothermic, is negligible. In order to explain this result, the long lived [CH2CHOH*+, CH3CHO] solvated ion was generated by reaction of the CH2CHOH*+ enol ion with (CH3CHO)n in the cell of a Fourier transform ion cyclotron resonance mass spectrometer. The structure of this solvated ion was clearly established. Labeling indicates that [CH2CHOH+, CH3CHO], upon low energy collisions, reacts by H* abstraction more rapidly than by H+ transfer to the neutral moiety. This shows that the entropic factors are determinant when the enol ion reacts directly with acetaldehyde.
van der Rest G
Laboratoire des Mecanismes Reactionnels, Ecole Polytechnique, Palaiseau, France.
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