The nature of intramolecular hydrogen bond in Naphthazarin

In this work, a feasible method has been introduced for investigating the proton tunneling frequency in Naphthazarin (NZ). A two-dimensional potential energy surface which couples OH stretching with in-plane bending modes has been computed for a firmed skeleton geometry, at the B3LYP/6-31G**, B3LYP/6-311G**, B3LYP/6-311 + + G** and MP2/6-31G** levels. This potential energy function is used to calculate the tunneling frequency, OH stretching, and in-plane bending frequencies. By calculations at the MP2/6-31G** level, the tunneling frequency of 15.3 and 0.9 cm(-1) and the barrier height of 65.3 kJ/mol was obtained for light and deuterated NZ for the stepwise proton transfer, respectively. Also, the tunneling frequency of 0.8 and 0.0 cm(-1) and the barrier height of 127.3 kJ/mol were obtained for the light and deuterated NZ for the concerted pathway, respectively. The obtained results indicate that both stepwise and concerted proton transfers pathways are probable.