Computation of polarizability, hyper-polarizability and hardness as descriptor for enol–keto tautomerizations of 2-hydroxy pyridines

Abstracts y functional theory (DFT) based calculations on a series of intra-molecular proton-transfer reactions e.g. 2-hydroxy pyridine (2HP), 5-methyl-2-hydroxy pyridine (5Me2HP) and 5-fluoro-2-hydroxy pyridine (5F2HP) are performed to understand the variation of the quantum chemical reactivity parameters e.g. polarizability, hardness, ionization potential along the proton transfer co-ordinate. Variations in optical gap and first hyper-polarizability which are measures of non-linear optical parameters are also computed along the proton transfer co-ordinate of the species. The average polarizability (αav), first hyper-polarizability (β), chemical hardness (η), ionization potential (I.P) and optical gap (ΔE) show their optimum value at the same IRC point which corresponds to the transition state (TS) for all the three titled intra-molecular proton transfer systems. The maximum polarizability and minimum chemical hardness at the transition state (TS) are due to greater extents of charge transfer which arise from smaller optical gap.