A study of the proton transfer of the nitro-substituted benzoic acids in water-dimethylsulfoxide mixtures compared with the same process in the gaseous phase.

A study of the proton transfer process from nitro-substituted benzoic acids to benzoic acid in H2O-DMSO mixtures compared with the same process in the gaseous phase is presented. A thermodynamic cycle allows calculation of a transfer process in solvent X which refers to a gaseous initial state, i.e. dDPi g->x. These thermodynamic quantities have been assumed as a measure of "external" solute-solvent interactions. It may be noted that in solution the resonance effect appears in the ortho-anion, while in the gaseous phase the resonance is effective for the para-compound. A comparison with the chloroisomers shows that the proton transfer process is easier for the nitro-isomers in the gas phase while the contrary is true in solution