Investigations on the Photochemical Reaction Mechanisms of Selected Dibenzoylmethane Compounds

Abstract

In this work, combined time-resolved spectroscopies of femtosecond transient absorption, nanosecond transient absorption, and DFT calculations were performed to unravel the photocyclization reaction mechanisms of selected dibenzoylmethane (DBM) derivatives, including 2-chloro-1,3-diphenylpropan-1,3-dione (1a), 2-chloro-1-(3,5-dimethoxyphenyl)-3-phenylpropan-1,3-dione (1b), 2-chloro-2-fluoro-1,3-diphenylpropan-1,3-dione (1c), and 2-chloro-2-fluoro-1,3-di­(4-methoxyphenyl)­propan-1,3-dione (1d). Photocyclization reaction mechanisms for 1a and 1b are similar, where a C–Cl heterolysis occurs yielding an α-ketocation intermediate, followed by cyclization to generate the cation species. On the other hand, 1c and 1d undergo dechlorination primarily producing a radical species, which further experiences cyclization yielding cyclized radical species. The dominant factor leading to the different reaction mechanisms is the involvement of a fluorine atom bonded at α-C. Due to the meta-effect, the p-methoxy substitution on the benzene ring inhibits the photocyclization reaction and reduces the yield of photocyclization.

Investigation of thia-Diels–Alder Reactions by Ultrafast Transient Absorption Spectroscopy and DFT Calculations

“…During the early times, the species appearing at 370 nm was ascribed to the singlet state of 2 (denoted as 2­(S 1 ) ), which then converted to a new species appearing at 490 nm and then decayed from 1.72 to 38.1 ps. A previous study on dibenzoylmethane compounds unraveled the intramolecular transfer of γ-hydrogen to oxygen to form the 1,4-diradical . Thus, the new species observed for 2 in fs-TA was tentatively attributed to the 1,4-diradical (labeled as 2-BR­(S 1 ) ).…”

“…A previous study on dibenzoylmethane compounds unraveled the intramolecular transfer of γ-hydrogen to oxygen to form the 1,4-diradical. 16 Thus, the new species observed for 2 in fs-TA was tentatively attributed to the 1,4-diradical (labeled as 2-BR(S 1 ) ). The above assignments were further confirmed by TD-DFT calculations, where the simulated UV–vis spectra of 2(S 1 ) and 2-BR(S 1 ) resembled the corresponding fs-TA spectra recorded at 217 fs and 15.3 ps, respectively ( Figures S5 and S6 ).…”

Solid–Liquid Equilibrium Behavior and Thermodynamic Analysis of Dibenzoylmethane in Different Pure and Binary Solvent Systems from 278.15 to 318.15 K

“…A dry sample of dibenzoylmethane presents a colorless oblique square sheet crystal. On the one hand, as a co-stabilizer of the calcium/zinc hydroxide stabilization system, it is used to make PVC mineral water bottles. , On the other hand, it can be used as an analytical reagent to verify carbon disulfide and thallium. , The quality of DBM is inseparable from the solution crystallization process, and solubility data are the basis of designing the solution crystallization process. Consequently, the measurement of solubility is crucial to the development of the solution crystallization process. , What’s more, the solubility data contribute to a greater understanding of the interactions between DBM and solvents and the thermodynamic properties of mixing, which are significant in physical chemistry. ,− However, there is no systematic study of DBM solubility in the literature.…”

“…On the one hand, as a co-stabilizer of the calcium/zinc hydroxide stabilization system, it is used to make PVC mineral water bottles. 7,8 On the other hand, it can be used as an analytical reagent to verify carbon disulfide and thallium. 7,8 The quality of DBM is inseparable from the solution crystallization process, and solubility data are the basis of designing the solution crystallization process.…”

“…7,8 On the other hand, it can be used as an analytical reagent to verify carbon disulfide and thallium. 7,8 The quality of DBM is inseparable from the solution crystallization process, and solubility data are the basis of designing the solution crystallization process. Consequently, the measurement of solubility is crucial to the development of the solution crystallization process.…”