The electron-induced trimerization of acrylic acid anion radical in the gas phase

In this work, the electron-induced reaction of acrylic acid was studied using an FT-ICR-Mass spectrometer and DFT calculations at M06-2X/aug-cc-pVTZ level of theory. The experiments showed the formation of acrylic acid trimer after 40 seconds as the major product. In the theoretical part, the structures and energies of various intermediates, transition states, and products were found via 4 different routes in five steps, consisting of electron transfer, proton transfer, dimerization, trimerization, and cyclization. The highest barriers belonged to the proton-transfer step, which defined the kinetic of the process and the kinetic product. The reactions were only possible up to the formation of the acyclic trimer and the cyclization process in the studied routes was kinetically and thermodynamically impossible. The calculated relative energies showed the possibility of two acyclic trimer structures as the major products. The first (I5-1), was the most stable and thermodynamic product with − 67.63 kcal/mol relative energy with a 12.38 kcal/mol overall barrier. The second (I5-2), was the kinetic product with a 10.55 kcal/mol barrier and − 55.21 kcal/mol relative energy versus the reactant. Because of the completion of the reaction in 40 s and at room temperature, the kinetic product was selected as the major product.