Natural Bond Orbital, Bond Order and Frequency based Study of Hydrogen Bond Formation in Different Glycols-Water Complex

Abstract

Natural bond orbital (NBO) analysis, natural atomic orbital (NAO) analysis, Wiberg bond order, vibrational frequency, free energy and enthalpy changes for hydrogen bond formation in different polyethylene glycol + water complex and dipropylene glycol + water complex have been performed by Hatree Fock (HF) method, second order Møller–Plesset perturbation theory (MP2) and Density Functional Theory (DFT) using 6-31++G(d,p) basis set. In order to describe hydrogen bond interaction appropriately, B3LYP DFT-D, WB97XD, M06 and M06-2X functionals having dispersion term are used. It is observed that the hydrogen bond in glycol + 1 water complex is found to be stronger when glycol act as proton donor as per charge differences and Wiberg bond order. Glycol water complex have shown higher red shift values for hydrogen bonded O-H bond stretching compared to that of water dimer. The glycols are found to be potential inhibitors for water cluster, as formation of glycol + 1 water complex and glycol + 2 water complex are favourable process at high pressure (10 atm) and low temperature (263 K, 273 K) according to thermochemical calculations.