An aldehyde is an organic compound with the functional group R–CHO. The functional group is a terminal carbon atom double bonded to oxygen, forming a carbonyl group, bonded to hydrogen and an R group. The R group can be a hydrogen atom, an alkyl or an aryl group. The group –CHO is known as an aldehyde group and is only found at the end of the carbon chain; a carbonyl group found within the carbon chain is part of the functional group of a ketone.
Aldehydes are common to organic chemistry and are an important feature, along with ketones, of carbohydrates. Aldehydes are fromed from the partial oxidisation of primary alcohols and form carboxylic acids when further oxidised.