carbonyl group

carbonyl group , in chemistry, functional group that consists of an oxygen atom joined by a double bond to a carbon atom. The carbon atom is joined to the remainder of the molecule by two single bonds or one double bond. If the carbonyl group is joined only to alkyl groups or aryl groups , the compound is a ketone ; if it is joined to at least one hydrogen atom, the compound is an aldehyde . The chemical reactivity of aldehydes and ketones is primarily due to the difference in electronegativity between carbon and oxygen. Because oxygen has the greater affinity for electrons, it acquires a partial negative charge, becoming electron-rich; the carbon atom of the carbonyl group thus becomes electron-deficient, acquiring a partial positive charge. One major type of reaction of aldehydes and ketones involves the addition of an electron-rich chemical species to the electron-deficient carbon atom of the carbonyl group. Another type of reaction is due to the tendency of the electron-deficient carbon atom of the carbonyl group to partially attract electrons from carbon atoms adjacent to it in the molecule, thus increasing the acidity of hydrogen atoms that are bonded to the adjacent carbon.

car·bon·yl / ˈkärbəˌnil/ • n. [as adj.] Chem. of or denoting the divalent radical =C=O, present in such organic compounds as aldehydes, ketones, amides, and esters, and in organic acids as part of the carboxyl group: carbonyl compounds. ∎  a coordination compound in which one or more carbon monoxide molecules are bonded as neutral ligands to a central metal atom: nickel carbonyl.

ketone Any one of a group of organic compounds that contain the carbonyl group (>C=O) linked to two hydrocarbon groups. The ketone group is a carbonyl group with two single bonds to other carbon atoms (–CO–). Examples are acetone (propanone), CH₃COCH₃, and methyl ethyl ketone (butanone), CH₃COC₂H₅. See also ketone body.