Steric and Electronic Effects on the Dehydration Step in Cyclohexanone and Bicyclic Ketones Oxime Formation

Between pH 4 and pH 13, oxime formation from hydroxylamine with cyclohexanone and bicyclic ketones proceeds with rate limiting dehydration of the addition intermediate which is in equilibrium with the ketone and hydroxylamine. The dehydration step exhibits catalysis by oxonium ion (pH 4 to ca. 8), a pH independent pathway (pH 8 to ca. 10) and catalysis by hydroxide ion (pH ca. 10 to 13). The steric and electronic effects give important insights into the structure of the transition state of the mechanisms of oxonium ion, hydroxide ion catalyzed and spontaneous reaction.