Collect. Czech. Chem. Commun. 1997, 62, 645-655

A New Iterative Method of Construction of the Hammett Acidity Function

Oldřich Pytela

Department of Organic Chemistry, University of Pardubice, 532 10 Pardubice, Czech Republic


A new iterative algorithm has been devised for construction of the H acidity function. The procedure is based on gradual transformation of the dependence of log I vs acid concentration into the dependence of H vs acid concentration, and it involves four steps. In the first step a continuous acidity function is obtained by taking the average of log I values for the same acid concentrations. The second step of the algorithm is smoothing out of the acidity function by means of smoothing the H value by weighted moving average. In the third step, the mean distances between the log I values and the corresponding values of the smoothed acidity function H are calculated for the given indicator, and in the fourth step these distances are used together with log I values for calculating a new acidity function. The procedure designed was converted into a programme in the Delphi 2 language for PC Pentium and was successfully validated on literature data.

Keywords: Acidity functions; Acidity function construction; Dissociation constants; Weak acids and bases.