Reaction Mechanism of 4‑Chlorobiphenyl and the NO<sub>3</sub> Radical: An Experimental and Theoretical Study

Experiment and theoretical chemistry calculations were conducted to elucidate the mechanism of the reaction between 4-chlorobiphenyl (4-CB) and the NO<sub>3</sub> radical. The degradation of PCBs was investigated mechanistically through transient absorption spectroscopy technology and high-accuracy theoretical calculation by using 4-CB as the model. Laser flash photolysis (LFP) experiments were performed at 355 nm. The main intermediate was analyzed through transient absorption spectroscopy and identified to be a charge transfer complex (CTC). The final products were identified through GC–MS analysis. The ground states and excited states of the reactants were calculated through density functional theory (DFT) method. The absorption bands at 400 and 700 nm show good agreement with the experimental results. The ratio of absorbance at 400 and 700 nm is 1.6, and the experimental value is 1.8. Analysis of the charge population indicated that one unit charge transfer from 4-CB to NO<sub>3</sub>. The entire reaction process was divided into two phases. In the first phase, the CTC intermediate was formed by electrostatic attraction between 4-CB and the NO<sub>3</sub> radical. In the second phase, the most important channel of subsequent reactions is the σ-complex as an intermediate formed by N–C coupling. The final product 4-chloro,2-nitrobiphenyl was generated with the breakage of B<sub>C–H</sub> and B<sub>N–O</sub>, and benzene derivatives were formed by other channels.