oxime

Oximes are organic compounds that feature the hydroxyimino functional group, with a general formula of R1R2C=NOH. They are formed by the condensation of a carbonyl compound (an aldehyde or a ketone) with hydroxylamine (NH2OH). The product contains a C=N–OH moiety and is typically referred to as an aldoxime (from aldehydes) or a ketoxime (from ketones). The C=N–OH bond can exhibit E/Z (cis/trans) isomerism depending on the orientation of the substituents around the C=N bond.

Preparation is usually achieved by reacting the carbonyl compound with hydroxylamine hydrochloride in the presence of a base (such as sodium acetate) in water or alcohol. The reaction removes water to form the oxime. Oximes are useful as protective derivatives for carbonyl compounds in synthesis and as intermediates in various transformations.

One important transformation is the Beckmann rearrangement, in which a ketoxime is converted under acidic conditions to an amide with migration of an adjacent substituent. Oximes can also be alkylated at oxygen to give oxime ethers. In analytical chemistry, oxime formation is used to derivatize carbonyl compounds to stabilize and facilitate detection, for example in gas chromatography and LC methods. In medicine, oximes play a role as antidotes for organophosphate poisoning, the best-known example being pralidoxime (2-PAM), which reactivates acetylcholinesterase.