MS18-P02 Structural Changes Induced By High Pressure And Radiation In Crystals Of Three Cinnamic Acid DerivativesThe [2+2] photodimerization was conducted in crystals of 2,5-difluorocinnamic (1), 3,5-difluorocinnamic (2) and 2,6-difluorocinnamic (3) acids in ambient and high-pressure conditions. The photochemical reaction was induced stepwise by UV/vis radiation and the X-ray diffraction experiment was carried out after each step. This enabled us to monitor changes in the unit cell parameters, intermolecular geometry and product content in crystals. The influence of pressure on the direction and size of those changes was analyzed .
For each compound there is a critical point below which the increasing pressure speeds up the reaction, and above which the reaction cannot be further accelerated. This is due to the changes in the geometrical parameters describing a pair of reacting molecules and the simultaneous decrease in the volume of free space.
The photochemical reactivity of three studied compounds changed in the following order: (1) > (2) > (3). To rationalize this observation we analyzed the parameters that could have an impact on the reactivity: the geometrical parameters for reacting molecules, intermolecular interactions, size and shape of free spaces in crystals and also the substituent effect. It turned out that the role of the substituent effect is important and should be considered during the studies of reactivity of cinnamic acids in crystals.
 Galica, T. et al. (2018). Cryst. Growth Des. 18, 1636−1644.Keywords: XRD, Photoreaction, high-pressure,