Collect. Czech. Chem. Commun. 1986, 51, 2143-2150

The Hammett substituent constants and effects of medium

Oldřich Pytela, Miroslav Ludwig and Miroslav Večeřa

Department of Organic Chemistry, Institute of Chemical Technology, 532 10 Pardubice


The dissociation constants measured earlier for 35 substituted benzoic acids in seven solvents (water, methanol, ethanol, dimethylformamide, acetonitrile, sulfolane, and acetone) have been submitted to the principal components analysis and the factor analysis to produce sets of the Hammett substituent constants. The solvent effects have been evaluated on the dissociation constants of the substituted benzoic acids and, hence, also on the respective substituent constants. He differences have been compared between the substituent constants determined by the principal components analysis and by the factor analysis, the latter being found to be more suitable. The obtained sets of substituent constants have been confronted with literature data, and an excellent agreement has been found between the σ constants derived from the measurements in water with the sets of primary substituent constants and some other sets.