The reasons for the photochemical behaviour of propylamine 4-(2,4,6-triisopropylbenzoyl)benzoate during the Norrish-Yang reaction

Abstract

The path of the Norrish-Yang reaction in crystals of propylamine 4-(2,4,6-triisopropylbenzoyl)benzoate was monitored under ambient pressure by means of single-crystal XRD experiments. The crystal structures containing product and reactant molecules in various proportions, i.e. for various stages of the reaction, were determined. The reaction was successfully monitored until 30% conversion. During the reaction, both o-isopropyl groups created product molecules, however, at different rates. In search of the reasons for such photochemical behaviour of reactant molecules, the intramolecular geometry, size and shape of free space and intermolecular interactions were analyzed. It occurred that the intermolecular interactions had the crucial significance for the reactivity. The progress of the Norrish-Yang reaction in crystals under a high pressure of 1.0 GPa was monitored based on the changes in the cell constants. The high-pressure structure of the pure reactant crystal was determined at 1.0 GPa. Comparison of high and ambient-pressure structures revealed a similarity in the intramolecular geometry and significant changes in the area of molecules, which can influence the photochemical behaviour of the compound at high pressure. The characteristics and the size of the structural changes brought about by the Norrish-Yang reaction are different at ambient and high pressures.