Statistical study of the influence of the hydroxyl groups in positions 3 and 4 on the ionization process of 3,4-dihydroxybenzoic acid

Abstract

The contributions of each of the two hydroxyl groups to the ionization and solvation processes for 3,4-dihydroxybenzoic acid were studied by considering the enthalpy values of these processes as a linear combination of those related to the same processes for the 2,3-dihydroxy and 2,4-dihydroxy derivatives in water-dimethylsulphoxide mixtures with the mole fraction of dimethylsulphoxide ranging from 0 to 0.8. For this purpose, diparametric and monoparametric regression analyses were used. In these analyses, the total standard deviations, slope and intercept standard deviations, correlation coefficients, null hypotheses a = 0, b = 0, r = 0 (where a is the intercept, b the slope and r the regression coefficient), the Student t test and F test of the above cited values were taken into account. Particular attention was paid to the presence of the so-called collinearity between the explanatory variables. The introduction of a hydroxyl group in position 3 destabilizes the benzene ring, overcoming the stabilization effect caused by the hydroxyl in position 4.