A DFT level quantum mechanical analysis of 4-Amino-3, 6-dichloro-2-pyridinecarboxylicacid (AMPYD) and 3, 6-Dichloro-2-pyridinecarboxylic acid (CLPYD) has been performed to explore their electronic, structural and spectral behavior. In this theoretical analysis various geometrical parameters, band gap and assignment of important vibration frequencies are reported and analyzed for both the compounds. In AMPYD the C-Cl bond lengths are found to be 1.84 A0 and 1.82 A0 while in CLPYD the C-Cl bond lengths are 1.83A0and 1.81A0. The C-C bonds of pyridine group of AMPYD are slightly longer than the C-C bonds of same group in CLPYD. It can be attributed to the presence of –NH2 group in AMPYD. The bond length suggests that AMPYD is more reactive than CLPYD. Analysis also suggest that the active sites in both the compounds are lies on C-Cl bonds and on C-C bond present between pyridine ring and the substitute group of same bond. Both the compounds get stabilized by hydrogen bonding. Bond angle analysis reveals that all the C and N atoms in both undertaken compounds are in SP2 hybridization. Analysis also suggests that O2 is in SP3 hybridization. Since all C and N atoms are in trigonal planer orientation therefore structure of both compounds should be planer. Analysis of dihedral angles reveals that in both undertaken compounds pyridine ring and substitute group are planer. Both the –Cl attached with ring are also planer to ring. In AMPYD, –NH2 group is also planer to ring. O1, O2, N1 and N2 are most negative elements while C3 and C6 are most positive elements it suggests maximum reactivity around C3-N2 and C6-O2 bonds. The total energyof the two compounds is found to be -1404.26 a.u. and -1349.20 a.u. The band gap in undertaken molecules is found to be 4.89 eV (253.54 nm) and 5.30 eV (233.93 nm) respectively. Therefore, AMPYD is more polar than CLPYD. Analysis also reveals that AMPYD is soft and highly reactive. Zero-point vibration energy for both AMPYD and CLPYD is found to be 263289.5 Joules/Mol and 218865.6 Joules / Mol. The stoichiometric formula for AMPYD and CLPYD are calculated as C6H4Cl2N2O2 and C6H3Cl2NO2 respectively and Deg. of freedom for both the compounds are 42 and 36 respectively. The dipole moment of AMPYD and CLPYD is computed as 6.22 and 3.61 Debye. Total thermal energy, Cv and entropy of AMPYD are computed as 69.691 Kcal / Mol, 39.716 Cal / Mol-kelvin, 104.545 Cal / Mol-kelvin, respectively and for CLPYD these values are computed as 58.255 Kcal / Mol, 34.072 Cal / Mol-kelvin, 99.027 Cal / Mol-kelvin, respectively.
