Energies of the gas-phase deprotonation of nitro-substituted benzenesulfonic and benzoic acids: The role of the conformation isomerism of sulfonic acids

• Published in: Russian Journal of Physical Chemistry A 2014-04, Vol.88 (4), p.661-666
• Main Authors: Ivanov, S. N., Giricheva, N. I., Nurkevich, T. V., Fedorov, M. S.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Physical Chemistry; Structure of Matter and Quantum Chemistry
• ISSN: 0036-0244; 1531-863X
• DOI: 10.1134/S0036024414040104

The Gibbs energies of deprotonation Δ r G 298 ○ of gaseous benzoic acid (BA), benzenesulfonic acid (BSA) and their six mono-, di-, and trinitro-substituted derivatives are calculated by means of B3LYP/cc-pVTZ and MP2/6-311++G**. The dependences of Δ r G 298 ○ on the number and the position of nitro groups in an aromatic ring are revealed, as is the possibility of intramolecular hydrogen bond (IHB) formation in ortho -substituted acids. It is found that the deprotonation of conformers of ortho -nitro-substituted BSA without IHBs requires less energy (by 4–5 kcal/mol) than for conformers with IHBs. It is shown that the Δ r G 298 ○ values for substituted BA are ∼22 kcal/mol higher than the corresponding values for substituted BSA. A trend of diminishing Δ r G 298 ○ for nitro-substituted acids is observed when the number of nitro groups is increased, and di- and trinitro-substituted BSA may therefore be considered superstrong acids.