Termolecular proton transfer reactions assisted by ionic hydrogen bond formation: Reactions of aromatic cations with polar molecules

Authors

George M. Daly, Virginia Commonwealth University
Michael Mautner, Virginia Commonwealth UniversityFollow
Y. B. Pithawalla, Virginia Commonwealth University
M. Samy El-Shall, Virginia Commonwealth UniversityFollow

Document Type

Article

Original Publication Date

1996

Journal/Book/Conference Title

The Journal of Chemical Physics

Volume

104

Issue

20

DOI of Original Publication

10.1063/1.471512

Comments

Originally published at http://dx.doi.org/10.1063/1.471512

Date of Submission

October 2015

Abstract

We present a new method that applies resonant‐two‐photon ionization to generate reactant ions selectively in the source of a high‐pressure mass spectrometer (R2PI‐HPMS) 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 ^+•)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 hydrogen‐bonded chains that facilitate fast subsequent proton extraction. Correspondingly, kinetic simulations suggest that the mechanism proceeds through (C₆H₆ ^+•)S+S→S₂H⁺+C₆H₅ ^• and C₆H₆ ^+•+2S→S₂H⁺+C₆H₅ ^•reactions, respectively. The rate coefficients of these reactions are in the range 10⁻¹³−10⁻¹² cm³ s⁻¹ for the reaction through a bimolecular switching channel and in the range 10⁻²⁶−10⁻²⁸ cm⁶ s⁻¹ for reaction through a direct termolecular proton extraction mechanism. The relation to energetics and reactant structure is examined.

Rights

Daly, G. M., Meot-Ner, M., & Pithawalla, Y. B., et al. Termolecular proton transfer reactions assisted by ionic hydrogen bond formation: Reactions of aromatic cations with polar molecules. The Journal of Chemical Physics, 104, 7965 (1996). Copyright © 1996 American Institute of Physics.

Is Part Of

VCU Chemistry Publications