A clear demonstration of the stereoelectronic effect of nitrogen in chloride ion loss by (E)- and (Z)-hydroximoyl chlorides

Abstract

(E)-Benzohydroximoyl chlorides have been examined for the first time and are shown to react (as the conjugate ion) > 10⁷-fold more slowly than the corresponding (Z)-benzohydroximoyl chloride anions. This large rate difference is attributed to the favourable antiperiplanar lone pair on the adjacent nitrogen which facilitates Cl^– loss from the (Z)-substrate. The (Z)-benzohydroximoyl chlorides were formed by direct chlorination of (E)- or (Z)-benzaldoximes while the (E)-chlorides were formed by acylation of these (Z)-isomers, photoisomerisation and separation, and then subsequent deacylation in situ.