Substituent effect on ionization potential, O-H bond dissociation energy and intra-molecular hydrogen bonding in salicylic acid derivatives

The ionization potential (IP), O-H bond dissociation energy (BDE) and intra-molecular hydrogen bonding in selected para-substituted salicylic acids, 5-R-SA, with R as -NO2, -CHO, -COOH, -halogen, -OH, -OCH3, -alkyl, -NH2, -NH(CH3), -N(CH3)2 and their radicals have been investigated by density functional theory with B3LYP functional in conjunction with 6-31G(d) and 6-311++G(d,p) basis sets. All the calculations have also been performed using BHLYP functional in conjunction with 6-311++G(d,p) basis set. A common order of IPs and BDEs for the studied 5-R-SAs is found as -NO2 > -COOH (-CHO) > -H > -OCH3 > -NH2 > -NH(CH3) > -N(CH3)2. The effect of substituents on the structure, charge distribution and intra-molecular hydrogen bond has also been discussed.