Model chemistry of hydrazides. II. Electronic structure of five-membered aromatic hydrazides

Abstract

The model chemistry of five-membered aromatic hydrazides at SEMO level of theory employing AM1, PM3, SAM1 and MNDO Hamiltonians has been studied using AMPAC 6.7 package. The effect of heteroatom (O, S or N) in cyclopentadiene and the position (2- or 3-) of hydrazide fragment on quantum chemical parameters are reported in the gaseous phase. The stability based on total energy follows the order furoic > thiophene> pyrrole hydrazides. The heat of formation (HoF) is exothermic for furoic hydrazide only. Pyrrole with hydrazide fragment in the second position has the lowest dipole moment of 1.93 Debye whereas the 3-analogue has 4.9 units. The second order hyperpolarizabilities are smaller, but greater than urea and thiourea. Based on the present values of third order hyperpolarizabilities, the effect of substituents throws light on utility of these compounds with non-linear optical properties. The shapes of these molecules, electrophilic centers and charge distribution are derived from 3D-surfaces and 2D-contours of total electron density (TD), electrostatic potential (ESP) and energies of frontier molecular orbitals (FMOs). Logarithm of partition coefficient, molecular refractivity and Henry's constants are also computed. These results offer complementary information in understanding the apparently contradictory physico-chemical properties and biological response of the hydrazides.