Controlling the action of chlorine radical: from lab to environment

Abstract

The strength of Bz—Cl˙ complexation has been explored using density functional theory (DFT) calculations, including dispersion-corrected (DFT-D) calculations. Of the methods tested, the ωB97X-D method seems the best performing, along with the previously tested MPW1K method. The effect of substituent (X = NO₂, F, Cl, Br, H, CH₃, OCH₃, OH, NH₂ and N(CH₃)₂) on the stabilities of the Ar—Cl˙ π-like intermediates show a good correlation with the linear free energy relationships used experimentally, but this is not the case for Ar—Cl˙ σ-complexes, suggesting the transition state of abstraction as being π-like in nature. The role of PAH and lignin derivatives in mediating chlorination reactions in nature is explored. Stable π-complexes were identified for lignin derivatives, indicating humic substances may mediate chlorine atom reactivity at the marine boundary layer, in addition to forming chlorolignins.