Photoreaction Kinetics of Cinnamate Salts - Influence of Cation and Halogen Substitution as Studied by Solid-State Nmr

Abstract

The photodimerization kinetics of potassium, rubidium and cesium cinnamate, with aromatic substitution by chlorine and bromine in the meta position, was studied by solid-state NMR. All salts photoreact to the corresponding truxinates with a non-planar cyclobutane ring. Analysis of the kinetics by the JMAK equation shows that the reaction rate is faster with smaller cation and in general chlorine salts react faster than the corresponding bromine salts. Data are analyzed based on the crystal structure, e.g., distance and orienation of reacting double bonds and halogen-halogen contacts. Furthermore, determination of the chemical shift anisotropy (CSA) tensor for reactant and product can provide information for necessary atomic reoientations in consequence of photoreaction. Results are explained based on the necessary movements of atoms between reactant and product.

Keywords: photodimerization kinetics, cinnamate salts, solid-state NMR