Search PubMed⌕ Search

Biomedical subjects

P Mourgues

Publications and source records attributed to P Mourgues.

5 recordsLinked to original sources
PubMed2003

Reactions of CH(3)CHO(.+) and of CH(3)COH(.+) with water upon Fourier transform ion cyclotron resonance conditions.

The reactions of CH(3)CHO(+) and of CH(3)COH(+) 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 CH(3)COH(+) into its more stable isomer CH(3)CHO(+), 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 [H(2)OH(+)...CH(3)(.)] and [H(2)OH(+)...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 [H(2)O...H(+)...H(2)N-C=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 [H(2)OH(+)...CH(3)CO] 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.

Journal Article↗
PubMed2001

Ter-body intermediates in the gas phase: reaction of ionized enols with tert-butanol.

In the gas phase, the CH2CHOH.+ enol radical cation 1 as well as its higher homologues CH3CHCHOH.+ 2 and (CH3)2CCHOH.+ 3, undergo exactly the same sequence of reactions with tert-butanol, leading to the losses of isobutene, water and water plus alkene. Fourier transform ion cyclotron resonance (FT-ICR) experiments using labeled reactants as well as ab initio calculations show that independent pathways can be proposed to explain the observed reactivity. For ion 1, taken as the simplest model, the first step of the reaction is formation of a proton bound complex which gives, by a simple exothermic proton transfer, the ter-body intermediate [CH2CHO., H2O, C(CH3)3+]. This complex, which was shown to possess a significant lifetime, is the key intermediate which undergoes three reactions. First, it can collapse to yield tert-butylvinyl ether with elimination of water. Second, by a regiospecific proton transfer, this complex can isomerize into three different ter-body complexes formed of water, isobutene and ionized enol. Within one of these complexes, which does not interconvert with the others, elimination of isobutene leads to the formation of a solvated enol ion. Within the others, a cycloaddition-cycloreversion process can proceed to yield the ionized enol 3 (loss of water and ethylene channel).

Journal Article↗
PubMed2000

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.

Journal Article↗
PubMed1999

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.

Journal Article↗