J.-F. Gal

Gas-phase structural (internal) effects in strong organic nitrogen bases

Gas-phase basicities (GB) of strong organic bases containing the imino group were re-examined in the light of the re-evaluated GB values for the reference bases given in a recent compilation of Hunter and Lias. Structural (internal) effects which influence the basicity are discussed and general relations for the GB prediction are proposed for simple alkyl amidines and guanidines. These relations were used for estimation of cyclization and intramolecular H-bonding effects. Copyright

Gas-phase lithium-cation basicities of some benzene derivatives: An experimental and theoretical study

Abstract The gas-phase lithium-cation basicities of a series of monosubstituted benzene derivatives, namely C 6 H 5 X (X=H, Me, CHCH 2 , OH, OMe, SH, Cl, Br) have been measured by means of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The structures of the corresponding complexes and their relative stabilities were investigated with B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) density functional theory calculations. In all cases, the π-complexes are favored with respect to those in which the metal monocation interacts with the substituent. These latter kind of complexes, which are entropically favored with respect to the π-complexes, are found to be chelated species, in which Li + bridges the heteroatom of the substituent and the ipso carbon atom. The Li + basicity of the benzene derivatives investigated reflects the electron-donor ability of the aromatic moiety as a function of the substituent. Consistently, there is a linear correlation between the Li + basicity and the frequency of the vertical displacement of Li + with respect to the aromatic ring.

On the Use of the Kinetic Method for the Determination of Proton Affinities by Fourier‐transform Ion Cyclotron Resonance Mass Spectrometry

The use in Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry of the collision-induced dissociation of proton-bound dimers, the kinetic method or Cookss method, is tested. This method is compared with the proton-transfer equilibrium method. Good agreement between the two methods is observed. Advantages and limitations of the FTICR kinetic method are briefly discussed.

The gas-phase basicity of ethyl-, ethenyl- and ethynylphosphines and arsines

Abstract The gas-phase basicities of the title compounds have been determined by Fourier transform ion cyclotron resonance mass spectrometry. Arsines are systematically weaker bases than phosphines. Basicity decreases in both series in the order ethyl > ethenyl > ethynyl. On the basis of their ionization energies, the phosphorus atom is recognized as the preferred site of protonation in the phosphines studied. A similar reasoning applied to arsines does not allow a clear-cut conclusion to be made. As it appears from the experimental results of this study and the few data on alkyl and phenyl derivatives available in the literature, substituent effects are attenuated by a factor of approximately 1.15 when going from phosphines to arsines.