I. Characteristics and classification
Carbonyl compounds contain in theirmolecule a bivalent functional group called carbonyl group.
Depending onthe substituents at the carbon atom of the carbonyl group carbonyl compounds are subdivided into aldehydes, ketones, carboxylic acids and functional derivatives of carboxylic acids.
The group - CHO, also called aldehyde group, is the functional group of aldehydes.
The carbonyl group in ketones is also called ketone group and it is the functional group of ketones.
The functional group in carboxylic acids is carboxyl group.
Functional derivatives ofcarboxylic acids are esters, anhydrides, acid (acyl) halides, acid amides, salts.
The functional group inallthese compounds is called acyl group.
The carbonyl group and carbonylcompounds are extremely important for living organism. Some representatives of aldehydes, ketones, quinones and carboxylic acids are given below.
II. Aldehydes and ketones
Aldehydes
Aldehydes can be considered as derivatives of hydrocarbons in which molecules two hydrogen atoms, attached to a carbon atom at the end of the chain, have been replaced by bivalent oxygen.
They have the general formula
where R is H, alkyl group or an aryl group. All aldehydes, except formaldehyde, have a hydrogen atom on one side of the carbonyl carbon and at least one carbon on the other side.
CH3-CH2-CH2–CHO butanal CH3-CH=CH–CHO 2-butenal
Ketones
Ketones have a formula
, where R and R' are alkyl or aryl groups. Depending on the type of hydrocarbon groups ketones can be aliphatic, aromatic and aliphatic-aromatic. There are ketoneswith two or more carbonyl groups in their molecules.
Aliphatic ketones
CH3–CO–CH3 propanone (dimethyl ketone, acetone)
CH3–CO–CH2–CH3 2-butanone (ethylmethyl ketone)
CH3–CO–CH2–CH2–CH3 2-pentanone
Aromatic ketones
C6H5-CO-C6H5 diphenyl ketone (benzophenone)
Aliphatic-aromatic ketones
C6H5-CO-CH3 methyl phenyl ketone (acetophenone)
More examples: