Reactivity of radical anions of nitro compounds during photochemical reduction

Abstract

It is a well-known fact that photochemical reduction reactions of nitro compounds are used in many fields of science and industry. However, there are factors that inhibit or nullify the total reaction process. Such a role is attributed to radical anions. The radical anions of nitrobenzene and 4-nitromethylbenzoate were considered. These molecules were studied by modern methods of quantum chemistry: BP, MP2, HF, calculations were carried out in quantum chemical program Orca 5.0.4. Russian and foreign works on the subject of research were studied and analysed, possible mechanisms of radical anion reactions of nitro compounds under different conditions were suggested. Geometrical parameters of the equilibrium molecule of a nitro compound and its radical anion were calculated, the correlation of the obtained data with the previously known ones was established. Reaction schemes with neutral molecules such as dimethyl sulfide were modelled. It was found that during the reaction the radical anion of a nitro compound led to slowing down of the photochemical reduction reaction, the process of hydrogen atom detachment from the substrate did not occur. The charge transfer from the radical anion to the dimethyl sulfide molecule in real time was considered. It has been found that the negative charge transfer to the dimethyl sulfide molecule and transition of the radical anion of a nitro compound to the initial state really occurs. The behaviour of the radical anion of a nitro compound in reactions with cations – proton-donor molecules – has been analysed. The practical role of the radical anions is enormous; a detailed study of the mechanism of its occurrence and reactivity makes it possible to study the mechanisms of photochemical reduction of nitro compounds fully.