∞ generated and posted on 2016.12.20 ∞
Oxygen that is double bonded to a carbon atom.
Carbonyl groups found on end carbons, that is, where the carbon is also bonded to a hydrogen atom, are known as aldehydes. Carbonyl group that are found on middle carbons, that is, where the carbon is also directly bonded to two different carbon atoms, are known as ketones. Functional groups of various sorts can also be found bonded to the same carbon that the carbonyl group is associated with, such as a hydroxyl group, thus giving rise to a carboxyl group.
Among biomolecules, carbonyl groups are most prominently associated with monosaccharides, particularly as seen the linear forms of those molecules. The end product of glycolysis, pyruvate, also possesses a carbonyl group. Other biomolecules also have carbonyl groups though often in combination with atoms other than hydrogen or carbon also bound to the same carbon atom as the carbonyl group.
Figure legend: A carbonyl group consists of a carbon atom to which three other atoms are bound, two of which are either carbon or hydrogen and the third is a double-bonded oxygen. If the carbon is a middle carbon, that is, if itself is bonded to two carbon atoms, then the presence of the carbonyl group give rise to what is known as a ketone. If one of the atoms is a hydrogen and the other is a carbon, then the molecule is an aldehyde. If both of the non-oxygen atoms are hydrogen then the molecule is formaldehyde. Things become a lot more complicated if something other than an H or C is bound the same carbon as the carbonyl group.
A carbonyl group provides some polarity to a molecule, that is, they can be described as polar groups.