THEORETICAL STUDY FOR COMPARISON OF pKa OF A NUMBER OF SCHIFF BASES BY EMPLOYING PARAMETERS DERIVED FROM DFT AND MP2 METHOD

Abstract

The ionization constants of seven compounds derived from Schiff bases have been studied theoretically. In this study, the factors affecting the ionization constant pKa of Schiff bases were found, which are van der Waals forces, energy levels, hardness, chemical potential and spherical electrophile index by conducting a theoretical study of these compounds using two methods of quantum mechanics for the purpose comparison, which is the Ab-initio basic calculation methods. Two methods were chosen, which are the density function theory (DFT) method and the MP2 Mueller-Pleist perturbation theory method using Chem program. Office 2008 the extent to which these two methods correspond to the known chemical bases was determined by discussing the theoretical variables that were calculated using the two methods referred to above and finding the relationship between the calculated physical variables with each other and determining their nature. After conducting the multiple statistical analysis process, it was found that the best variables that affect the ionization constant in the DFT method are (Bond C1-C7, Bend, VDW) and the rest of the variables were theoretically excluded because the coefficients of those variables are very few or equal to zero and accordingly these variables were adopted to obtain A relationship with better results, as it is noted that the values of the correlation coefficient in this DFT method are (0.994). As for the MP2 method, the best variables that affect the ionization constant are (Ƞ, KE, Tors) and the rest of the variables were theoretically excluded because the coefficients of these variables are very few or equal Therefore, these variables were adopted to obtain a relationship with better results, as it is noted that the values of the correlation coefficient in this MP2 method are (0.989). By comparing the theoretical values with the practical values, it was found that the results of the DFT method were closer to the process than the results of the MP2 method.