Hydroxylimino

Hydroxylimino refers to a functional group with the structure R2C=NOH, where R represents any organic substituent or hydrogen atom. This group is also known as an oxime. Oximes are derivatives of aldehydes and ketones where the carbonyl oxygen is replaced by a hydroxylimino group. The formation of oximes is a common reaction in organic chemistry, typically achieved by reacting an aldehyde or ketone with hydroxylamine or its salts, often under acidic conditions. This reaction is a condensation, releasing a molecule of water.

The nitrogen atom in the hydroxylimino group is sp2 hybridized and is bonded to one organic group (or hydrogen) and a hydroxyl group. This arrangement leads to the possibility of cis-trans isomerism (also known as E/Z isomerism) around the carbon-nitrogen double bond, provided that the two substituents on the carbon atom are different and the nitrogen atom is bonded to two different groups (which is the case with the hydroxyl group). These isomers, syn and anti oximes, can have different chemical and physical properties.

Oximes are important intermediates in organic synthesis. They can be reduced to primary amines, rearranged to amides (Beckmann rearrangement), or undergo other transformations. Their properties and reactivity depend on the nature of the R groups attached to the carbon atom and the stereochemistry of the C=N double bond. They find applications in analytical chemistry for the detection and quantification of carbonyl compounds and as ligands in coordination chemistry.