Küçük peroksitlerin fotokimyasal parçalanmaları ve enerji yüzeyleri

Organic peroxides are known to have important roles in many chemical and biochemical processes e.g. as intermediates in the oxidation of various hydrocarbons with oxygen, as initiators of free-radical polymerization and cross-linking agents, in lipid oxidation, and in DNA damage and mutation. Thus, study of the organic peroxides and their radicals are of fundamental interest and importance. Although several reaction pathways after dissociation of organic peroxides have been successfully identified using time-resolved optical absorption spectra, interpretation of these data can be complicated due to spectral overlap of parent molecules, intermediates, and products. Therefore, a combined experimental-theoretical investigation is necessary in case of complex or less studied systems. In this study, we tried to identify the thermal dissociation pathways in photodissociation of diethyl peroxide, di-tert-butyl peroxide and dicumyl peroxide by locating all local minima and the connecting transition states in their photochemical dissociation. We used DFT approach with M06-2X functional which was found to be suitable for calculations of equilibrium geometries, relative energies and electronic excitation energy values. We compared calculated DFT energies with CCSD(T) level energies which was shown to have no additional information. As observed experimentally, methyl radical abstraction is the main dissociation mechanism for studied peroxides after O-O bond breaking. This reaction was found to have the least activation energy in all studied peroxides. By locating all local minima and transition states for the secondary reactions, we are able to construct the energy landscapes of the peroxide dissociation and their general characteristics. For our results to be comparable to experimental time-resolved UV-Vis absorption spectra, we used TDDFT/PCM method for calculating electronic excitation energies in the presence of acetonitrile and ethanol solvents. Shifts in electronic excitation energies of studied radicals in these solvents were found to be similar and negligible.