[Show abstract][Hide abstract] ABSTRACT: Collision-induced dissociation (CID) of Li(+) adducts of three sets of compounds that contains an amide bond, including 2-(4, 6-dimethoxypyrimidin-2-ylsulfanyl)-N-phenylbenzamide, its derivatives and simpler structures was investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Observed fragment ions include those that reflect loss of LiOH. Other product ions result from the Smiles rearrangement and direct C-S bond cleavage. MS/MS of H/D exchange products demonstrated occurrence of a 1,3-H shift from the amide nitrogen atom to the phenyl ring of these compounds. The LiOH loss from Li(+) adducts of amides was further examined by CID of [M + Li](+) ions of N-phenylbenzamide and N-phenylcinnamide. Loss of LiOH was essentially the sole fragmentation reaction observed for the former. For the latter, both losses of LiOH and H(2)O were discovered. The presence of electron-donating substituents of the phenyl ring of these compounds was found to facilitate elimination of LiOH, while that loss was retarded by electron-withdrawing substituents. Proposed fragment ion structures were supported by elemental compositions deduced from ultrahigh resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MS/MS) m/z value determinations. Density functional theory-based (DFT) calculations were performed to evaluate potential mechanisms for these reactions.
Full-text · Article · May 2012 · Journal of the American Society for Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: The elimination of SO2 from deprotonated sulfonamides in the negative ion mode was confirmed by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) experiments. For a set of N-arylbenzenesulfonamides substituted at the para position of the arylamine, the ln([M-H-SO2](-)/[M-H]-) values were correlated with the sigmap(-) substituent constants but, instead of a linear relationship, a bent line was obtained. Analyses of the complex curve led to the identification of two competing routes, which were further investigated by Hartree-Fock theoretical calculations. Furthermore, collision-induced dissociation (CID) of deprotonated N-alkylbenzenesulfonamides containing the -CHCHNHSO2- structure yielded a [M-H-66](-) product ion This characteristic ion could help to distinguish the side-chain isomers.
No preview · Article · Sep 2008 · Rapid Communications in Mass Spectrometry
[Show abstract][Hide abstract] ABSTRACT: The negative ions of deprotonated 2-(4, 6-dimethoxypyrimidin-2-ylsulfanyl)-N-phenylbenzamide and its derivatives are studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Upon collisional activation, the [M−H]− ions dissociate in two competitive pathways that can be considered as the gas-phase Smiles rearrangement reactions, giving rise to the characteristic fragment ions [M−H−C7H4OS]− and [M−H−C13H8NSR]− (R=substituent). Theoretical computations were invoked to shed light on the reaction mechanisms of the representative Compound 1 by the semiempirical PM3 method. These theoretical calculations show that the formation of [M−H−C13H8NSR]− (R=H for Compound 1) is more favorable. Furthermore, it is found that the intensities of the two product ions are strongly influenced by the position and the nature of the substituents. For the para-substituted compounds, the ln[(M−H−C7H4OS−)/(M−H−C13H8NSR−)] values are well correlated with the σ
p− substituent constants. In addition, the dependence of the intensity ratios of these two ions, ln[(M−H−C7H4OS−)/(M−H−C13H8NSR−)](R=CH3), on the collision energy can be used to distinguish the positional isomers.
Full-text · Article · Nov 2007 · Journal of the American Society for Mass Spectrometry