M. Decouzon

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.

Fourier transform mass spectrometric studies of isovalent rare earth ions Sc+, Y+ and Lu+ with methanol. Formation of dimethoxide—metal species M(OCH3)+2

Abstract The primary and subsequent gas-phase reactions between methanol and the isovalent rare earth metal ions Sc + , Y + and Lu + have been investigated using a Fourier transform ion cyclotron resonance mass spectrometer. The three metal ions react exothermically with methanol. Among the primary reaction products obtained, only two are common to the three metals, the hydroxide—metal ions MOH + , and the methoxide—metal ions MOCH + 3 . For Sc + and Y + , as primary products the metal oxide ions MO + , and the metal—formaldehyde complexes M(OCH 2 ) + , are also observed, as well as the formation of the metal—dihydride ion MH + 2 (only for Y + ). All the primary ions undergo subsequent reactions with methanol, and the final product is always the M(OCH 3 ) 2 (CH 3 OH) + n species ( n = 0–3). The results are analysed to yield the lower and/or upper limits for bond energies: D °(M + OH) and D °(HOM + OH) > 92 kcal mol −1 , D °(HOM + OCH 3 ) and D °(M + OCH 3 ) > 105 kcal mol −1 for M  and Lu, D °(HOSc + OCH 3 ) and D °(Sc + OCH 3 ) > 119 kcal mol −1 , D °(ScOH) −1 , D °(YOH) −1 , and D °(LuOH) −1 .

Lithium-cation and proton affinities of sulfoxides and sulfones: A fourier transform ion cyclotron resonance study

The kinetic method was used for the quantitative determination of lithium-cation affinities by Fourier transform ion cyclotron resonance. This method was applied to a series of XYSO and XYSO2 compounds. Proton basicities of the SO and SO2 compounds were also determined. When comparison is made between Li+ basicities and proton basicities, a linear regression encompassing XYSO and XYSO2 families suggests that Li+ may be bonded in a similar way to the SO and SO2 moieties, that is, to only one oxygen on the latter. PM3 calculations support this hypothesis.

Gas-phase reactivity of rare earth cations with phenol: competitive activation of C–O, O–H, and C–H bonds

The gas-phase reactions of Sc+, Y+, and Ln+ (Ln=La-Lu, except Pm) ions with phenol were studied by Fourier transform ion cyclotron resonance mass spectrometry. All the ions except Yb+ were observed to react with the organic substrate, activating O-H, C-O, and/or C-H bonds, with formation of MO+, MOH+, and/or MOC6H4+ ions as primary products. The product distributions and the reaction efficiencies obtained showed the existence of important differences in the relative reactivity of the rare earth metal cations, which are discussed in terms of factors like the electron configurations of the metal ions, their oxophilicity, and the second ionization energies of the metals. The primary product ions participated in subsequent reactions, yielding species such as M(OH)(OC6H5)+, which lead mainly to M(OC6H5)2(HOC6H5)n+ ions, where n=0–2. Formation of M(OC6H5)(HOC6H5)n+ species was also observed in the case of the metals that have high stabilities of the formal oxidation state 2+, Sm and Eu.

Gas-phase reactions of Sc+, Y+, and Lu+ with alcohols. Effects of the class and chain length of alcohols on the nature of primary products

The primary gas-phase reactions between methanol, ethanol, propan-1-ol, propan-2-ol, and 2-methyipropan-2-ol and the isovalent rare earth metal ions Sc+, Y+, and Lu+ generated by laser desorption-ionization of metal targets have been investigated by using a Fourier transform ion cyclotron resonance mass spectrometer. The three metal ions react exothermically with all the alcohols. The overall reactivity is controlled by the high oxophilicity of these metals, and the primary metallated ions obtained are principally oxygenated species. However, the number and the nature of these primary products depends on the electronic configuration of the metal ions as well as on the class and the principal chain length of alcohols. The order of reactivity is Y+ > Sc+ > Lu+. The Y+ and Sc+ ions principally react via C—O and O—H insertions, whereas Lu+ reacts by direct abstraction or via various five-center electrocyclic mechanisms as a function of the class and the alcohol chain length.

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.

Fourier transform-ion cyclotron resonance study of the gas-phase acidities of germane and methylgermane; bond dissociation energy of germane

An accurate gas-phase acidity for germane (enthalpy scale, equivalent to the proton affinity of GeH3−), ΔHacido(GeH4) = 1502.0 ± 5.1 kJ mol−1, is obtained by constructing a consistent acidity ladder between GeH4, and H2S by using Fourier transform-ion cyclotron resonance spectrometry, and 0 and 298.15 K values for the first bond dissociation energy of GeH4 are proposed: D0o(H3Ge-H) = 352 ± 9 kJ mol−1; Do(H3Ge-H) = 358 ± 9 kJ mol−1, respectively. These results are compared with experimental and theoretical data reported in the literature. Methylgermane was found to be a weaker acid than germane by approximately 35 kJ mol−1: ΔHacido = 1536.6 kJ mol−1.

Fourier transform ion cyclotron resonance determination of lithium cation basicities by the kinetic method: upward extension of the scale to phosphoryl compounds

Lithium cation basicities (LCBs) are reported for a series of 16 phosphoryl compounds, including phosphine oxides, phosphinates, phosphonates and phosphates The experiments were carried out using the kinetic method applied to Fourier transform ion cyclotron resonance mass spectrometry. Two different data treatments of the Napierian logarithm of ion peak intensity ratios were compared: extrapolation to zero kinetic energy and weighted averaging of data over the range of energies studied. The effect of pressure on the LCB determinations was also studied. An increase in the pressure of the collision gas allows one to decrease the collision energy necessary for efficient dissociation of the lithium-bonded dimer, thus favoring the fragmentation pathway of lowest energy. Among the monofunctional ligands, the phosphoryl derivatives studied have the largest LCBs yet known. The previously published self-consistent LCB scale of Taft and co-workers was extended upward by 14 kJ mol -1 .

The gas-phase acidity and bond dissociation energies of hydrogen telluride

The gas-phase acidity of hydrogen telluride, ΔH⦵acid (H2Te) = 331.3±0.8 kcal/mol−1, is obtained from ion/molecule reaction equilibria using FT-ICR mass spectrometry. The gas-phase acidities of the four hydrogen chalcogenides correlate with the reciprocals of the corresponding hydrogen—heavy atoms bond distances. From thermochemical cycles the two bond dissociation energies are calculated [D(HTeH) = 66.2 ± 1.2 kcal mol−1, D(TeH) = 61.2 ± 1.6 kcal mol−1]. As for the other members of the series, breaking the first bond is significantly more endothermic than breaking the second.