Jean Francois Gal

Gas-phase basicity of simple amides toward proton and lithium cation: an experimental and theoretical study

The gas-phase lithium cation basicities (LCBs) of the six amides RC(O)NRR (R, R = H or Me) were reexamined by means of Fourier transform ion cyclotron resonance mass spectrometry and using the kinetic method. LCBs for HCONH2, MeCONH2 and MeCONHMe were reevaluated. The new set of experimental data was found to be consistent with the expected methyl-substitution effects. For a series of compounds including the six amides and H2CO, MeCHO and Me2CO, density functional theory calculations of LCBs and gas-phase proton basicities (GBs) at the B3LYP level reproduce satisfactorily the trend of substitution effects.

Reliability of Fourier transform-ion cyclotron resonance determinations of rate constants for ion/molecule reactions

The results of gas-phase rate constant measurements by Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry may be influenced by the setting of instrumental parameters. The effects of pressure, ionization duration, ionization energy, selection of the parent ion, mass range, trapping potential, reaction delay and pumping-regulation-valve opening have been investigated and analysed using a two-level Plackett–Burman statistical design which is described in an appendix. This approach was tested on the ion/molecule reaction between acetyl ion and acetone: CH3CO+ + CH3COCH3 → CH2CO + (CH3COCH3)H+. Although space-charge effects are known to be deleterious to FT-ICR, this is the first study demonstrating, on a statistical basis, the necessity of parent ion selection for obtaining reliable rate constants. Considered independently, the other factors tested do not appear statistically significant, but the possibility of interactions among them is discussed. The mean of the rate constants from experiments with acetyl ion selection, kabs = (2.14 ± 0.18) × 10−10 cm3 molecule−1 s−1, is compared with literature data.