Noémie Dechamps

Decarboxylation of metastable methyl benzoate molecular ions

By using a combination of mass spectrometric methodologies and density functional theory calculations [DFT/B3LYP/6-311 ++ G(d, p)], it is proposed that the decarboxylation of metastable methyl benzoate molecular ions occurs via distonic and ion-neutral complex (INC) intermediates. The same INC involving a complex between the benzyl radical and protonated carbon dioxide is also generated upon decarboxylation of metastable phenylacetic acid molecular ions. Internal proton transfer within the INC produces in fine a mixture of toluene and isotoluene radical cations.

Ion-Molecule Reactions Involving Methyl Isocyanide and Methyl Cyanide

Ion–molecule reactions involving methyl isocyanide and methyl cyanide have been performed in a new rf-only hexapole collision cell inserted in a large-scale tandem mass spectrometer. Beside protonation processes, N-methyl cyanogen ions (CH3N+CCN) and 1-methyleneiminium-1-ethylenium ions (CH2CN+CH2) have been produced in high yield and fully characterized by high-energy collisional activation. The unimolecular chemistry of the molecular ions of caffeine (1,3,7-trimethyl xanthine) has been revisited on the basis of these new results.

Gas-Phase Nitrosation of Ethylene and Related Events in the C2H4NO + Landscape

The C2H4NO(+) system has been examined by means of quantum chemical calculations using the G2 and G3B3 approaches and tandem mass spectrometry experiments. Theoretical investigation of the C2H4NO(+) potential-energy surface includes 19 stable C2H4NO(+) structures and a large set of their possible interconnections. These computations provide insights for the understanding of the (i) addition of the nitrosonium cation NO(+) to the ethylene molecule, (ii) skeletal rearrangements evidenced in previous experimental studies on comparable systems, and (iii) experimental identification of new C2H4NO(+) structures. It is predicted from computation that gas-phase nitrosation of ethylene may produce C2H4(*)NO(+) adducts, the most stable structure of which is a pi-complex, 1, stabilized by ca. 65 kJ/mol with respect to its separated components. This complex was produced in the gas phase by a transnitrosation process involving as reactant a complex between water and NO(+) (H2O.NO(+)) and the ethylene molecule and fully characterized by collisional experiments. Among the other C 2H 4NO (+) structures predicted by theory to be protected against dissociation or isomerization by significant energy barriers, five were also experimentally identified. These finding include structures CH3CHNO(+) (5), CH 3CNOH (+) ( 8), CH3NHCO(+) (18), CH3NCOH(+) (19), and an ion/neutral complex CH2O...HCNH(+) (12).