The
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.
Laboratoire des Mecanismes Reactionnels, Ecole Polytechnique, Palaiseau, France.
van der Rest G
P
Mourgues
H
Nedev
HE
Audier