13 research outputs found
Termolecular proton transfer reactions assisted by ionic hydrogen bond formation: Reactions of aromatic cations with polar molecules
We present a new method that applies resonantâtwoâphoton ionization to generate reactant ions selectively in the source of a highâpressure mass spectrometer (R2PIâHPMS) for kinetic and equilibrium studies. Applications to reactions that would be obscured otherwise in a complex system are illustrated in mixtures of benzene with polar solvent molecules (S). We observe a novel type of proton transferreactions from C6H6 +⢠to two S molecules where S=CH3CN, CH3OH, C2H5OH and CH3COOC2H5, and from C6H5CH3 +⢠to two S molecules where S=CH3OH and C2H5OH to form protonated solvent S2H+ dimers. The reactions are driven by the strong hydrogen bonds in the S2H+ dimers and therefore require the formation of the hydrogen bond concertedly with proton transfer, to make the process energetically feasible. The adducts (C6H6 +â˘)S are observed with blocked solvent molecules where the subsequent switching reaction to yield S2H+ is slow, but not with alcohol reactants that can form hydrogenâbonded chains that facilitate fast subsequent proton extraction. Correspondingly, kinetic simulations suggest that the mechanism proceeds through (C6H6 +â˘)S+SâS2H++C6H5 ⢠and C6H6 +â˘+2SâS2H++C6H5 â˘reactions, respectively. The rate coefficients of these reactions are in the range 10â13â10â12 cm3âsâ1 for the reaction through a bimolecular switching channel and in the range 10â26â10â28 cm6âsâ1 for reaction through a direct termolecular proton extraction mechanism. The relation to energetics and reactant structure is examined