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1. Taming the Chlorine Radical: Enforcing Steric Control over Chlorine-Radical-Mediated C-H Activation

   https://doi.org/10.1021/jacs.1c13333  

   Gonzalez, Miguel; Gygi, David; Qin, Yangzhong; Zhu, Qilei; Johnson, Elizabeth J.; Chen, Yu-Sheng; Nocera, Daniel G. (January 2022, Journal of the American Chemical Society)

   Chlorine radicals readily activate C-H bonds, but the high reactivity of these intermediates precludes their use in regioselective C-H functionalization reactions. We demonstrate that the secondary coordination sphere of a metal complex can confine photoeliminated chlorine radicals and afford steric control over their reactivity. Specifically, a series of iron(III) chloride pyridinediimine complexes exhibit activity for photochemical C(sp(3))-H chlorination and bromination with selectivity for primary and secondary C-H bonds, overriding thermodynamic preference for weaker tertiary C-H bonds. Transient absorption spectroscopy reveals that Cl center dot remains confined through formation of a Cl center dot larene complex with aromatic groups on the pyridinediimine ligand. Furthermore, photocrystallography confirms that this selectivity arises from the generation of Cl center dot within the steric environment defined by the iron secondary coordination sphere. 

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2. Different chlorine and hydroxyl radical environments impact m-xylene oxidation products

   https://doi.org/10.1039/D3EA00024A  

   Bhattacharyya, Nirvan; Modi, Mrinali; Jahn, Leif G.; Hildebrandt Ruiz, Lea (August 2023, Environmental Science: Atmospheres)

   Transportation emissions of aromatic hydrocarbons such as xylenes evolve in the atmosphere due to radical oxidation and can form a variety of products, including secondary organic aerosol (SOA). 

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3. Degradation and Deactivation of Bacterial Antibiotic Resistance Genes during Exposure to Free Chlorine, Monochloramine, Chlorine Dioxide, Ozone, Ultraviolet Light, and Hydroxyl Radical

   https://doi.org/10.1021/acs.est.8b04393  

   He, Huan; Zhou, Peiran; Shimabuku, Kyle K.; Fang, Xuzhi; Li, Shu; Lee, Yunho; Dodd, Michael C. (February 2019, Environmental Science & Technology)

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4. Photocatalytic C–H activation and the subtle role of chlorine radical complexation in reactivity

   https://doi.org/10.1126/science.abd8408  

   Yang, Qiaomu; Wang, Yu-Heng; Qiao, Yusen; Gau, Michael; Carroll, Patrick J.; Walsh, Patrick J.; Schelter, Eric J. (May 2021, Science)

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   The functionalization of methane, ethane, and other alkanes derived from fossil fuels is a central goal in the chemical enterprise. Recently, a photocatalytic system comprising [Ce IV Cl 5 (OR)] 2− [Ce IV , cerium(IV); OR, –OCH 3 or –OCCl 2 CH 3 ] was disclosed. The system was reportedly capable of alkane activation by alkoxy radicals (RO•) formed by Ce IV –OR bond photolysis. In this work, we present evidence that the reported carbon-hydrogen (C–H) activation of alkanes is instead mediated by the photocatalyst [NEt 4 ] 2 [CeCl 6 ] (NEt 4 + , tetraethylammonium), and RO• are not intermediates. Spectroscopic analyses and kinetics were investigated for C–H activation to identify chlorine radical (Cl•) generation as the rate-limiting step. Density functional theory calculations support the formation of [Cl•][alcohol] adducts when alcohols are present, which can manifest a masked RO• character. This result serves as an important cautionary note for interpretation of radical trapping experiments. 

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5. Significant impact of heterogeneous reactions of reactive chlorine species on summertime atmospheric ozone and free-radical formation in north China

   https://doi.org/10.1016/j.scitotenv.2019.133580  

   Qiu, Xionghui; Ying, Qi; Wang, Shuxiao; Duan, Lei; Wang, Yuhang; Lu, Keding; Wang, Peng; Xing, Jia; Zheng, Mei; Zhao, Minjiang; et al (November 2019, Science of The Total Environment)