[Show abstract][Hide abstract] ABSTRACT: An increasing number of fluorinated drugs, pesticides, and fine chemicals are now produced and applied, especially those containing polyfluorinated aromatic moieties. However, at present, the extent of literature covering the special mass spectrometric behaviors of these compounds remains limited. Herein, we report an unexpected but also general gas-phase dissociation mode of polyfluorinated aromatics in mass spectrometry: expulsion of difluorocarbene (50-Da neutral loss). Results from accurate mass measurements, tandem mass spectrometric experiments, and density functional theory (DFT) calculations support an intramolecular F-atom “ring-walk” migration mechanism for gas-phase CF2 loss. Based on an assessment of the electron ionization-mass spectrometry (EI-MS) data of more than 40 polyfluorinated aromatic compounds from the National Institute of Standards and Technology data bank, we generalized on the substitution group effects on the difluorocarbene dissociation process of polyfluorinated aromatic compounds in EI-MS. These studies have enriched our knowledge of the special gas-phase reactivity of polyfluorinated aromatics and will provide valuable information in further analytical research of these compounds by mass spectrometry.
Full-text · Article · Sep 2013 · Journal of the American Society for Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: Gas phase decarbonylation and cyclization reactions of protonated N-methyl-N-phenylmethacrylamide and its derivatives (M·H(+)) were studied by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). MS/MS experiments of M·H(+) showed product ions were formed by loss of CO, which could only occur with an amide Claisen rearrangement. Mechanisms for the gas phase decarbonylation and cyclization reactions were proposed based on the accurate m/z measurements and MS/MS experiments with deuterated compounds. Theoretical computations showed the gas phase Claisen rearrangement was a major driving force for initiating gas phase decarbonylation and cyclization reactions of M·H(+). Finally, the influence of different phenyl substituents on the gas phase Claisen rearrangement was evaluated. Electron-donating groups at the para-position of the phenyl moiety promoted the gas phase Claisen rearrangement to give a high abundance of fragment ions [M - CO + H](+). By contrast, electron-withdrawing groups on the phenyl moiety retarded the Claisen rearrangement, but gave a fragment ion at m/z 175 by loss of neutral radicals of substituents on the phenyl, and a fragment ion at m/z 160 by further loss of a methyl radical.
Full-text · Article · Sep 2012 · Journal of the American Society for Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: Electrospray ionization triple quadrupole mass spectrometry (ESI-TSQ-MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) were used to investigate the interesting gas-phase reactions of the cationic iron (Fe) complexes of 2-pyrimidinyloxy-N-arylbenzylamines (1-6), which are generated by ESI when mixing their methanolic solutions. Further studies of these Fe complexes by collision-induced dissociation (CID) show that Fe(III) complexes undergo an interesting gas-phase single electron transfer (SET) reaction to give 1(•+) -6(•+) ,with loss of neutral FeCl(2) , whereas Fe(II) can catalyze gas-phase Smiles rearrangement reactions of compounds 1-6. By using different Fe(II)X(2) salts (X = Cl or Br) with a set of reactants, the role of the counterion (X(-) ) and the structure effect of the reactants on Fe(II)-catalyzed gas-phase Smiles rearrangement reactions are studied. Evidence obtained from by TSQ-MS and FTICR-MS experiments, hydrogen/deuterium (H/D) exchange experiments and theoretical computations supported some unique gas-phase chemistries initiated by introduction of Fe(II) into 1. Importantly, by comparing the distinct gas-phase reaction results of the cationic Fe(III) complexes with those of Fe(II) complexes, the charge state effects of iron on the gas-phase chemistries of Fe complexes are revealed.
Full-text · Article · Jan 2011 · Rapid Communications in Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: The CH(3)OH solutions of pyrimidinyloxy-N-arylbenzylamines (1-5) in the presence of Mg(II)X(2) salts (X = Cl or ClO(4)) were investigated by electrospray ionization mass spectrometry and tandem mass spectrometry (MS/MS) subsequently, showing that the cationic Mg(II) complexes 1-5·MgX(+) were important active complexes or intermediates for initiating interesting Smiles rearrangement reactions in both the gas and solution phases. By using different MgX(2) salts and selecting a set of reactants with different substitutes, the role of the counter-ion (X(-)) and the structure effect of the reactants on the Mg(II) catalyzed Smiles rearrangement reactions were studied. Moreover, the solvent effect on Mg(II) catalyzed Smiles rearrangement reactions was revealed by studying the CH(3)OH adduct complexes of 1-5·MgCl(+), which showed that the coordination of CH(3)OH to the Mg(II) center in the complexes decreased the reaction tendency. The mechanisms involved in the gas-phase Mg(II) catalyzed Smiles rearrangement reactions were proposed on the basis of MS/MS experiments and theoretical computations, showing some unique chemistries initiated by introducing Mg(II) into the template molecules.
Full-text · Article · Jan 2011 · European Journal of Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: The gas-phase synthesis of hydrodiphenylcyclopropenylium from alkali-cationized alpha,alpha'-dibromodibenzyl ketone (1) via nonclassical Lewis-acid-induced Favorskii rearrangement has been studied by electrospray ionization/tandem mass spectrometry (ESI-MS/MS) and theoretical methods, showing that cations [1-Br](+) by debromination from 1 and 1.M(+)(M = Li or Na) by alkali-metal cationization of 1 could convert into the protonated diphenylcyclopropenone 2.H(+) by collision-induced dissociation in the gas phase. A concerted mechanism for the Lewis-acid-induced Favorskii rearrangement from alkali-metal-cationized alpha,alpha'-dibromodibenzyl ketone was proposed and studied, based on mass spectrometric results and theoretical methods.
Full-text · Article · Sep 2010 · Rapid Communications in Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: The gas-phase rearrangement reactions of compound 1, 2-dimethoxypyrimidinyloxybenzylaminoben- zenedipropylurea, were studied by ESI-MS/MS. The experimental results showed that introduction of dipropylurea moiety into the molecule initiated various interesting gas-phase chemistries and the mechanisms were proposed on the basis of hydrogen/deuterium (H/D) exchange experiments and theoretical computations. Moreover, product 2, the solution-phase rearrangement product of compound 1, was synthesized and its gas-phase chemistries were also studied to support the propos gas-phase rearrangement reactions of compound 1.
Full-text · Article · Sep 2010 · Chinese Journal of Chemistry