Reactions of doubly deprotonated 2,6-naphthalenedicarboxylic acid with alcohols: Proton transfer versus solvation

George N. Khairallah, Matthew M. Meyer, Richard A.J. O'Hair, Alireza Fattahi, Jacob Schmidt, Steven R. Kass

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Electrospray ionization of 2,6-naphthalenedicarboxylic acid readily affords its doubly deprotonated dicarboxylate dianion (12−). This species clusters with background water and added alcohols in an ion trap at ∼10−3 Torr. Sequential solvation is observed to afford mono and dicoordinated ions. Surprisingly, the latter cluster (12−• 2TFE) is protonated by 2,2,2-trifluoroethanol (TFE) whereas 12−and 12−• TFE are not even though ΔH°acid(TFE) = 361.7 ± 2.5 kcal mol−1 (as given in the NIST website at http://webbook.nist.gov) and the B3LYP/6-31+G(d,p) proton affinities are 384.7 (12−), 377.6 (12−• TFE), and 362.7 (12−• 2TFE) kcal mol−1. That is, only the weakest base in this series, and the dianion with an equal number of solvent molecules and charged sites, undergoes proton transfer. In a FTMS instrument at lower pressures (∼10−8 Torr) inefficient proton abstraction is observed with the monosolvated dianion. This difference, and the observed reactivities of 12−, 12−• TFE and 12−• 2TFE are rationalized with the aid of computed potential energy surfaces. The chemical structures of these cluster ions were also probed via collision-induced dissociations, infrared photodissociation from 2700 to 3200 cm−1, and extensive calculations. All of the TFE species are found to be solvated dianions, but incipient proton transfer to afford electrostatically defying anion-anion clusters is noted in two cases. In proton transfer reactions, formation of the conjugate acid as a solvated ion lowers the energy of the system and reduces the Coulomb repulsion barrier facilitating the overall process.

Original languageEnglish (US)
Pages (from-to)180-187
Number of pages8
JournalInternational Journal of Mass Spectrometry
Volume418
DOIs
StatePublished - Jul 2017

Bibliographical note

Funding Information:
Support from the National Science Foundation and the Minnesota Supercomputer Institute for Advanced Computational Research are gratefully acknowledged. We thank the Australian Research Council (ARC) for financial support through the ARC CoE program (RAJO) and grants DP1096134 (to GNK) and DP150101388 (RAJO).

Publisher Copyright:
© 2016 Elsevier B.V.

Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.

Keywords

  • Cluster anions
  • Dianion
  • Gas-phase ion-molecule reactions
  • IRMPD
  • Microsolvation

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