Polarizability, hardness and electrophilicity as global descriptors for intramolecular proton transfer reaction path

Potential energy (PE) curves for intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 1-hydroxy-2-acetonaphthone (1H2AN) is studied using DFT-B3LYP/6-31+G(d,p) and TD-DFT/6-31+G(d,p) level of theory respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer in 1H2AN. Excited states PE calculations support the viability of ESIPT process in 1H2AN. Here, for the first time, polarizability, chemical hardness and electrophilicity are being used as global reactivity descriptors to locate the transition state for intermolecular proton transfer process. Both the minimum polarizability principle (MPP) and maximum hardness principle (MHP) are being obeyed along the intrinsic reaction co-ordinate (IRC) for intramolecular proton transfer process. We have also raised the decade old issue i.e. the use of O–H distance of enol tautomer as proton transfer co-ordinate instead of IRC. Our computation of these global reactivity descriptors along the proton transfer co-ordinate support intrinsic reaction coordinate (IRC) as the effective proton transfer co-ordinate, instead of variation of O–H distance of enol tautomer.