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Microhydration of Benzoic Acid Molecule and its Dissociation

Abstract

Proton transfer from the benzoic acid molecule to solvent water molecules occurs only when at least eight water molecules are attached to the benzoic acid, forming a hydrated cluster. Geometrical parameters, bond dipole moments and proton transfer parameter of hydrated clusters of benzoic acid, C6H5COOH.nH2O (n = 1-8) are calculated applying first principle based electronic structure theory. While the calculated solvent stabilization energy increases linearly with the increase in number of solvent water molecules in the hydrated clusters, interaction energy shows characteristic features of acid dissociation. O-H bond dipole moment of benzoic acid also show characteristic features of acid dissociation. Free energy of formation of the hydrated acid systems is calculated at different temperatures and pressures, and the hydrated systems are found to be stable at low temperature and pressure (100K/1╬╝Torr). Calculated O-H bond stretching frequency of the acid molecule shows red-shift with increase in number of water molecules in the hydrated clusters. Calculated hydrogen bond energy for breaking O-H bond of the acid molecule and forming O-H bond with solvent water molecule supports the observed fact that at least eight water molecules are needed for dissociation of benzoic acid. Number of water molecules required to dissociate a number of studied acid molecules is observed to be linearly correlated with their pKa values. Thus, in a non-thermodynamic route, one can predict pKa value of an acid.

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Publication details

The article was received on 14 Apr 2017, accepted on 09 Jun 2017 and first published on 09 Jun 2017


Article type: Paper
DOI: 10.1039/C7NJ01245D
Citation: New J. Chem., 2017, Accepted Manuscript
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    Microhydration of Benzoic Acid Molecule and its Dissociation

    K. Parvathi and D. K. Maity, New J. Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7NJ01245D

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