A theoretical study on protonation of some halogen substituted pyridine derivatives.

The geometries of 12 multi-halogenated pyridine derivatives were optimized using theoretical methods. The Hartree-Fock (HF) method with the 6-31G(d) and B3LYP method with 6-31G(d) basis sets were found to be adequate in calculation of absolute acidity constants, pK(a) values. A perfect correlation between the computed and experimentally obtained acidity constants, pK(a) values, was observed.

Quantum chemical studies on protonation of some substituted thiazole derivatives.

The acidity constants, pK(a) values for protonation of some substituted thiazole derivatives were calculated by using AM1 and PM3 basis sets of semi-empirical methods and B3LYP/6-31G(d) basis sets of density functional theory (DFT) calculated physical and thermodynamic parameters. Correlation search among the experimental and calculated acidity constants, pK(a) values, revealed that the best correlation exist between the experimental and ab initio calculated pK(a) values with a regression of R(2)=0.98.