KETONE

any of a class of organic compounds characterized by the presence of a carbonyl group in which the carbon atom is covalently bonded to an oxygen atom. The remaining two bonds are to other carbon atoms or hydrocarbon radicals (R): Ketones are highly reactive, although less so than aldehydes, to which they are closely related. Much of their chemical activity results from the nature of the carbonyl group. Ketones readily undergo a wide variety of chemical reactions. A major reason is that the carbonyl group is highly polar; i.e., it has an uneven distribution of electrons. This gives the carbon atom a partial positive charge, making it susceptible to attack by nucleophiles, which are species attracted to positively charged centres. Typical reactions include oxidation-reduction and nucleophilic addition. The polarity of the carbonyl group affects the physical properties of ketones as well. Ketones can be synthesized by a wide variety of methods. Because of their ease of preparation, relative stability, and high reactivity, ketones are nearly ideal chemical intermediates. Many complex organic compounds are synthesized using ketones as building blocks. Only a small number of ketones are manufactured on a large scale in industry. They are most widely used as solvents, especially in industries manufacturing explosives, lacquers, paints, and textiles. They are also used in tanning, as preservatives, and in hydraulic fluids. The most important ketone is acetone (CH3COCH3), a liquid with a sweetish odour. It is used primarily as a solvent in paints and lacquers and for cellulose plastics. Ketone compounds have important physiological properties. They are found in several sugars and in compounds for medicinal use, including natural and synthetic steroid hormones. Molecules of the anti-inflammatory agent cortisone contain three ketone groups.