Quantum-chemical investigation of the dependence of pKa on the calculated energy of proton removal for certain derivatives of indole and phenol
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The total energies of derivatives of N-hydroxyindole, indole, and phenol, and of their corresponding anions have been estimated with the aid of ab initio calculations on the 3-21G basis. The energies of proton removal were calculated from the difference in total energies of the appropriate anions and molecules. By comparing the calculated energies of proton removal with experimental values of pKa (acidity characteristic) a practically linear dependence was shown for the acidity characteristic on the energy of proton removal for the series of compounds investigated. An empirical formula has been proposed expressing the dependence of pKa on the energy of proton removal, which makes it possible to predict pKa in this series by carrying out calculations of the energy of proton removal (transfer).
KeywordsN-hydroxyindole indole anion 3-21G basis depronation acidity ab initio calculations
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