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Molecular calculations with the nonempirical ab initio modpot, vrddo, and modpot/vrddo procedures. VIII. charge delocalization in the anions of aromatic carboxylic acids and phenolic compounds
Author(s) -
Kaufman Joyce J.,
Popkie Herbert E.,
Preston Harry J. T.
Publication year - 2009
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560140822
Subject(s) - deprotonation , chemistry , delocalized electron , ab initio , computational chemistry , aromaticity , molecule , molecular orbital , ab initio quantum chemistry methods , valence (chemistry) , ion , organic chemistry
Nonempirical ab initio MODPOT/VRDDO calculations were performed on both the neutral molecules and the deprotonated anions of lipophilic aromatic acids and phenolic compounds. MODPOT/VRDDO results agree essentially to the third decimal place for orbital energies and population analyses with completely ab initio results using the same atomic valence basis set. The calculational results supported the hypothesis that there would be significant delocalization of the negative charge in the deprotonated anions. In the neutral aromatic carboxylic acids and phenolic compounds there is already an excess of electron density on the O atom. When the proton is removed from the O atom, the resulting negative charge is considerably delocalized over the molecule and not localized on the O atom from which the proton was removed. Only about 0.06 e extra remains on the O atom in a deprotonated anion of phenolic‐type compound or on the O in the deprotonated OH of the carboxylic group of an aromatic acid.