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.

Reactions of silyl cations with ketones in the gas phase

In the gas phase, (CH(3))(3)SiOSi(+)(CH(3))(2) and (CH(3))CH(2)SiOSi(+)(CH(3))(2) ions 1 and 2 were formed in the external source of a Fourier transform ion cyclofrom resonance (FT-ICR) spectrometer by electron impact ionization of (CH(3))(3)SiOSi(CH(3))(3). In the FT-ICR cell, the electrophilic center of these ions reacts with acetone to give product ions whose structures are probed by comparison with those of the products formed by reaction with water. The mechanisms of formation of these products, studied by labeling, involve facile 1,3-methyl transfer from silicon to silicon and cyclic intermediates. Copyright 1999 John Wiley & Sons, Ltd.

Insights into the C(4)H(8)(+.) potential energy surface: fourier transform ion cyclotron resonance studies of ion-molecule reactions of D-labeled partners

Reactions of [ethylene](+.) with ethylene and of [acetylene](+.) with ethane were studied by Fourier transform ion cyclotron resonance spectrometry using labeled reactants. The results confirm and clarify the different steps of the mechanism proposed previously and elaborated with other methods. The [[acetylene](+.), ethane] system can either dissociate to give the ethyl cation product, or isomerize into [[ethylene](+.), ethylene]. The latter system can either dissociate to yield ionized ethylene or convert into ionized but-2-ene, which undergoes a complete H-exchange prior to dissociation, leading to methyl radical, hydrogen radical and ethylene losses. The transfers of labeled atoms and the existence of H-exchange prior to formation of the products were used as a probe to check the different steps of the mechanism. The influence of the initial energy of the system on the reaction pathway is discussed. Copyright 1999 John Wiley & Sons, Ltd.