Compounds formed by reaction between hydroxylamine and an aldehyde RCOH+H2NOH → RCH:NOH+H2O If R is an aliphatic group, the aldoxime is generally a liquid or low-melting solid. If R is aromatic, the aldoxime is a crystalline solid. Aldoximes have a planar structure and can exist in two isomeric forms. In the syn form, the OH group is on the same side of the double bond as the H. In the anti form the OH and H are on opposite sides. Typically, aliphatic aldehydes give anti aldoximes; aromatic aldehydes give syn aldoximes.
RCOH+H2NOH → RCH:NOH+H2O