Reduction and radical addition: A theoretical study on chlorobenzonitriles

The three isomers of chlorobenzonitrile (CBN) and the corresponding radical anions are investigated by semiempirical methods in order to study the reg ioselectivity of solvated hydrogen and hydroxy radical attacks. Additional negative charge is distributed upon reduction at the chlorine and cyano sub units and in para-position to the cyano group. Most of the negative charge (about 7056) is located in the aromatic ring. The different protonation sit es for the negatively charged radical and neutral species are explained by distinctly different electro-negativities. The observed position of a hydro xy radical attack on 2-chlorobenzonitrile is correlated to the relative sta bilities of the six possible addition products. The electron density contri bution of 2-CBN as calculated by the Mulliken population analysis method is in excellent agreement with the experimentally observed formation of diffe rent products: The 2-chloro-5-hydroxybenzonitrile is the preferentially cre ated species, with both the 4- and 6-hydroxy isomers as important sideprodu cts.