Dear student,
A carbonyl group is a chemically organic functional group composed of a carbon atom double-bonded to an oxygen atom --> [C=O] The simplest carbonyl groups are aldehydes and ketones usually attached to another carbon compound. These structures can be found in many aromatic compounds contributing to smell and taste.
The carbonyl carbon atom, which is sp2-hybridized, contributes one electron to each of the three hybrid orbitals, forming three σ bonds. Formaldehyde has two σ bonds with hydrogen atoms and one σ bond with the carbonyl oxygen atom.
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