Kinetics of Photo-Oxidation of Oxazole and its Substituents by Singlet Oxygen

Ultrafast Valence-Electron Dynamics in Oxazole Monitored by X-ray Diffraction Following a Stimulated X-ray Raman Excitation

Direct imaging of the ultrafast quantum motion of valence electrons in molecules is essential for understanding many elementary chemical and physical processes. We present a simulation study of valence-electron dynamics of oxazole. A valence-state electronic wavepacket is prepared with an attosecond soft X-ray pulse through a stimulated resonant X-ray Raman process and then probed with time-resolved off-resonant single-molecule X-ray diffraction. We find that the time dependent diffraction signal originates solely from the electronic coherences and can be detected by existing experimental techniques. We thus provide a feasible way of imaging electron dynamics in molecules. Moreover, the created electronic coherences and subsequent electron dynamics can be manipulated by the resonant X-ray Raman excitation tuned to different core-excited states.

Mechanistic Insight into the Reactivities of Aqueous-Phase Singlet Oxygen with Organic Compounds

Singlet oxygen (¹O₂) is a selective reactive oxygen species that plays a key role for the fate of various organic compounds in the aquatic environment under sunlight irradiation, engineered water oxidation systems, atmospheric water droplets, and biomedical systems. While the initial rate-determining charge-transfer reaction mechanisms and kinetics of ¹O₂ have been studied extensively, no comprehensive studies have been performed to elucidate the reaction mechanisms with organic compounds that have various functional groups. In this study, we use density functional theory calculations to determine elementary reaction mechanisms with a wide variety of organic compounds. The theoretically calculated aqueous-phase free energies of activation of single electron transfer and ¹O₂ addition reactions are compared to the experimentally determined rate constants in the literature to determine linear free-energy relationships. The theoretically calculated free energies of activation for the groups of phenolates and phenols show excellent correlations with the Hammett constants that accept electron densities by through-resonance. The dominant elementary reaction mechanism is discussed for each group of compounds. As a practical implication, we demonstrate the fate of environmentally relevant organic compounds induced by photochemically produced intermediate species at different pH and evaluate the impact of predicting rate constants to the half-life.

Silver Benzoate Facilitates the Copper-Catalyzed C-N Coupling of Iodoazoles with Aromatic Nitrogen Heterocycles

In the literature, C-N coupling methods for the reaction of iodo-oxazole with 2-pyridinone were found to be low yielding. C-N coupling using silver benzoate additives with CuI catalysts and 4,7-dimethoxy-1,10-phenanthroline ligands has been developed to afford synthetically useful yields of the desired heterobicycle product. The reaction conditions are applied to the coupling of a range of iodo-heterocycles with 2-pyridinone. The coupling of a variety of NH-containing heterocycles with 4-iodo-oxazole is also demonstrated. The use of 2-, 4-, or 5-iodo-oxazole allows for the coupling of pyridinone to each oxazole position.