Two of the quantum mechanical methods, semi-empirical calculation represented by the AM1 model and an Abinitio method DFT, were used to accomplish a theoretical study to estimate the ionization constant (pKa) for several benzaldoximes substitution(BS). During the discussion of the theoretical variables selected for achieving thy study by the two ways mentioned above, the results showed that the methods of basic calculations (Abinitio) were more suitable than the semi-empirical method for such calculation, and the relationship between the observed and calculated parameters was determined together with their experimental values.

The relationship between the theoretically calculated (pKa) and their experimental values have been determined. These theoretically calculated variables were correlated using the two methods (DFT, AM1)with the values of pKa calculated experimentally by using multi parameters and linear regression analysis by trial and error. The results obtained by correlation were well indicated by the values of the correlation coefficient (R2) and standard deviation (SE) values in each method and the large agreement between the practical pKa values with the theoretical computed values. The great convergence between the theoretical pKa values and the practical values for both methods(AM1, DFT) indicates the suitability and accuracy for such calculation applied in this paper.