Theoretical Calculations of pKa Values for Substituted Carboxylic Acid

Abstract

Six different methods of determination have been used for studying ten derivatives of carboxylic compounds. Semi-empirical (AM1 and PM3), Hartree Fock (HF/STO-3G and HF/3-21G), and Density Function Theory (DFT/STO-3G and DFT/6-31G) were employed to calculate many physical theoretical parameters. The calculated data were correlated with experimental values of pKa using different regression(enter, stepwise and simple regression). Depending on the Fisher values, (HF/STO-3G) was shown as the best method for predicted of the pKa data compare to the (PM3) method using enter method. While (HF/3-21G)method has a big value of fisher compared with(PM3) using (stepwise) and (simple) methods. So, Multiple linear regression was performed to obtain the best prediction values using (enter) compare with (stepwise), and the two methods are the best compared with simple regression.