کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5134232 | 1492214 | 2017 | 8 صفحه PDF | دانلود رایگان |

- A dicarboxylate dianion clusters with alcohols.
- Sequential solvation is observed.
- Surprisingly, the weakest base undergoes proton transfer.
- Solvation of the conjugate acid results in a kinetically enhanced process.
- Coulomb barriers can be mitigated by cluster formation.
Electrospray ionization of 2,6-naphthalenedicarboxylic acid readily affords its doubly deprotonated dicarboxylate dianion (12â). This species clusters with background water and added alcohols in an ion trap at â¼10â3Â Torr. Sequential solvation is observed to afford mono and dicoordinated ions. Surprisingly, the latter cluster (12â
- 2TFE) is protonated by 2,2,2-trifluoroethanol (TFE) whereas 12âand 12â
- TFE are not even though ÎH°acid(TFE) = 361.7 ± 2.5 kcal molâ1 (as given in the NIST website at http://webbook.nist.gov) and the B3LYP/6-31+G(d,p) proton affinities are 384.7 (12â), 377.6 (12â
- TFE), and 362.7 (12â
- 2TFE) kcal molâ1. 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 (â¼10â8Â Torr) inefficient proton abstraction is observed with the monosolvated dianion. This difference, and the observed reactivities of 12â, 12â
- TFE and 12â
- 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 3200Â cmâ1, 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.
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Journal: International Journal of Mass Spectrometry - Volume 418, July 2017, Pages 180-187