The compound with carbonyl carbon linked to hydrogen and alkyl group is called aldehyde (RCHO), and the -CHO in the structure is called the aldehyde group. The lower aldehyde is liquid, the higher aldehyde is solid, and only methyl aldehyde is gas. The chemical properties of aldehyde are active, which can react with NaHSO3, H2, NH3 and so on, and can be easily oxidized to the corresponding carboxylic acid by weak oxidant. The structural characteristics of aldehyde molecules are that they contain aldehyde groups, which can catalyze the hydrogenation reduction to alcohol, and are easily oxidized by strong oxidants or even weak oxidants. The aldehyde groups are both oxidizing and reducing. Aldehydes have a wide range of uses. Methyl aldehyde vapor can disinfect the air, and the solution can be used for the preservation of biological specimens. Fat aldehydes generally have anesthetic and hypnotic effects. For example, chloral hydrate is an early synthetic hypnotic.