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 regioselectivity of solvated hydrogen and hydroxy radical attacks. Additional negative charge is distributed upon reduction at the chlorine and cyano subunits and in para-position to the cyano group. Most of the negative charge (about 70%) is located in the aromatic ring. The different protonation sites for the negatively charged radical and neutral species are explained by distinctly different electro-negativities. The observed position of a hydroxy radical attack on 2-chlorobenzonitrile is correlated to the relative stabilities of the six possible addition products. The electron density contribution of 2-CBN as calculated by the Mulliken population analysis method is in excellent agreement with the experimentally observed formation of different products: The 2-chloro-5-hydroxybenzonitrile is the preferentially created species, with both the 4- and 6-hydroxy isomers as important sideproducts