1. Cyanohydrin: Compounds possessing hydroxyl and cyano groups on the same carbon atom, ie. gem-hydroxy nitrates are called cyanohydrin. These are produced by addition of HCN to aldehydes or ketones in weakly basic medium.
2. Acetal: Compounds in which the two alkoxy groups are present on the terminal carbon atom are called acetals. These are produced by the action of an aldehyde with two equivalents of a mono hydric alcohol in presence of dry HCl gas.
3. Semicarbazone: These are derivatives of aldehydes and ketones, and are produced by action of semicarbazide on them in weakly acidic medium.
4. Aldol: Aldols are β- hydroxy aldehydes and are produced by the condensation of two molecules of the same or one molecule each of two different aldehydes in presence of a dilute aqueous base such as NaOH, KOH, Ba(OH)2 etc For eg:
5. Hemiacetal: They are gem-alkoxy alcohol. These are produced by addition of one molecule of a monohydric alcohol to an aldehyde in presence of dry HCl gas.
