Polarizability, chemical hardness and ionization potential as descriptors to understand the mechanism of double proton transfer in acetamide dimer

The double proton transfer mechanism in the acetamide dimer is examined in terms of the energy profile, reaction force, chemical hardness, average polarizability, ionization potential, chemical potential and interaction energies using HF as well as density functional theory based approach. The energy profile for the activation process of acetamide dimer to the imino ether product is obtained using B3LYP function and is in agreement with the results of the other methods. To test the validity of the reaction mechanism, the intrinsic reaction coordinate (IRC) calculation is performed at the B3LYP level of theory. The results show that the reaction starts with a structural rearrangement, where the two dimers approach each other, and through the transition state (TS) product is obtained. This structural rearrangement to the activation barrier steers the activation process. During the course of double proton transfer reaction in acetamide dimer (AAD) we observe that the ionization potential (IP) is inversely related with average polarizability (αav) and linearly related with chemical hardness (η). We also observe that the use of NH distance as proton transfer co-ordinate nicely explain the reaction energy profile and it is computationally less expensive than the IRC method.