Intramolecular hydrogen bond in ortho-hydroxyazobenzenes

Abstract

The intramolecular hydrogen bonding in ortho-hydroxyazobenzenes has been studied by means of CNDO/2 calculations. The strength of the hydrogen bonding is calculated as 8–9 kcal mol^–1(1 kcal ≈ 4.184 kJ) and compares well with the available experimental data. Some structural features associated with the formation of hydrogen bonding, such as charge redistribution, dipole moment and molecular orbital energies, are discussed. An energy partitioning analysis is employed to analyse bond structures within the six-membered hydrogen-bonded ring. The hydrogen bonding is generated from positive resonance and coulombic interactions mainly between the proton atom and the electron-donating nitrogen atom. The one-centre energy term and the exchange energy term are destabilizing for hydrogen-bond formation.