Theoretical Study of Hydrogen-Bonded Complexes of Chlorophenols with Water or Ammonia:  Correlations and Predictions of pKa Values

A simple practical method for predicting the acidity constants (as pKa values) of chlorophenols is proposed based on density functional theory calculations of a series of hydrogen-bonded complexes of phenol and 19 different congeners of chlorophenol, with a single probe molecule, either water or amm...

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Bibliographic Details
Published in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2005-02, Vol.109 (6), p.1159-1167
Main Authors: HAN, Jun, DEMING, Richard L., TAO, Fu-Ming
Format: Article
Language:English
Subjects:
Algorithms
Ammonia - chemistry
Chlorophenols - chemistry
Hydrogen Bonding
Hydrogen-Ion Concentration
Models, Chemical
Thermodynamics
Water - chemistry
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Summary:A simple practical method for predicting the acidity constants (as pKa values) of chlorophenols is proposed based on density functional theory calculations of a series of hydrogen-bonded complexes of phenol and 19 different congeners of chlorophenol, with a single probe molecule, either water or ammonia. Relevant structural parameters and molecular properties of these complexes, primarily involving the acidic hydroxyl group, are examined and plotted against the known pKa values of 14 chlorophenols and phenol. Strong linear correlations are found for these compounds. Such correlations are used to determine the pKa values of five chlorophenols whose experimental acidities have large uncertainties. Similar predicted pKa values are obtained by using different structural parameters and molecular properties for the complexes with either probe molecule. The study may be extended to determine the acidity of other compounds with a single acidic functional group.
ISSN:1089-5639
1520-5215
DOI:10.1021/jp045936z