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

Khairallah, G. N ; Sharif University of Technology | 2016

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  1. Type of Document: Article
  2. DOI: 10.1016/j.ijms.2016.09.005
  3. Publisher: Elsevier B.V , 2016
  4. Abstract:
  5. Electrospray ionization of 2,6-naphthalenedicarboxylic acid readily affords its doubly deprotonated dicarboxylate dianion (1 2-). 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 (1 2- • 2TFE) is protonated by 2,2,2-trifluoroethanol (TFE) whereas 1 2-and 1 2- • TFE are not even though δHacid(TFE)=361.7±2.5kcalmol-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 (1 2-), 377.6 (1 2- • TFE), and 362.7 (1 2- • 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 1 2-, 1 2- • TFE and 1 2- • 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 3200cm-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
  6. Keywords:
  7. Cluster anions ; Dianion ; Gas-phase ion-molecule reactions ; IRMPD ; Microsolvation
  8. Source: International Journal of Mass Spectrometry ; 2016 ; 13873806 (ISSN)
  9. URL: http://www.sciencedirect.com/science/article/pii/S1387380616301579