Functional Groups with a Carbon–Oxygen Double Bond (Carbonyl Groups)

Carbonyl groups are present in a large majority of organic compounds and in practically all biological molecules. These compounds behave similarly in many respects but differ depending on the identity of the atoms bonded to the carbonyl-group carbon. Aldehydes have at least one hydrogen bonded to the C=O, ketones have two carbons bonded to the C=O, carboxylic acids have an  OH group bonded to the C=O, esters have an ether-like oxygen bonded to the C=O, thioesters have a sulfide-like sulfur bonded to the C=O, amides have an amine-like nitrogen bonded to the C=O, acid chlorides have a chlorine bonded to the C=O, and so on. The carbonyl carbon atom bears a partial positive charge(δ+), and the oxygen bears a partial negative charge (δ-).