A theoretical study of the intramolecular proton transfer and calculation of the nucleus independent chemical shift in juglone and some of its derivatives

In the present study, first, the intramolecular proton transfer (IPT) process of juglone and its derivatives were theoretically investigated in the gas phase and the effect of electron-withdrawing and electron-releasing substi- tuents in different positions of the phenyl and benzoquinone rings of juglone on the IPT process was studied in which the geometries, energies and thermody- namic functions of the compounds were obtained using density functional theory (DFT) calculations at the B3LYP/6-31+G(2d,p) level. Next, the influ- ence of IPT on changing the aromaticity of the phenyl and benzoquinone rings was investigated. To determine the aromaticity of the rings, nuclear indepen- dent chemical shift (NICS) values were calculated for the ground state and transition state structures (GS1, TS and GS2) using the continues set of gauge transformations (CSGT) procedure at the B3LYP/6-311+G(2d,p) level.