Carbonyl group (ketone). Image credit: Flickr
Carbonyl group (ketone). Image credit: Flickr

A part of organic chemistry, a carbonyl group (C=O) is a functional group that comprises a double bond between a carbon and oxygen atom, and two R groups individually attached to the carbon atom. The R group could comprise hydrogen or carbon atoms, or any other element. Generally, the R group’s identity is unknown, unless it’s clearly mentioned what makes up the R group.

The oxygen atom is more electronegative compared to the carbon because it has a couple of lonely electron pairs hanging around. This means the oxygen atom has a much stronger pull in the bonding. In other words, electrons move from carbon to oxygen. This chemical structure contributes to the smell and taste and can be found in several aromatic compounds (such as benzene). Ketones, aldehydes, carboxylic acid, amide, carbonate, carbamate, carbamide (urea), etc. are types of molecules that comprise carbonyl groups and are called carbonyl compounds.

Polarity

A carbonyl group is polar, which means it carries both negative and positive charges. The carbon atom end of the carbonyl group has a marginal positive electrical charge, thanks to the loss of electrons to oxygen. This means the carbon is an electrophile (having electron deficiency and the state of being attracted to electrons) and can be targeted by a nucleophile (an ion or molecule that offers an electron pair).

The oxygen atom end, on the other hand, has a minor negative charge. This molecular arrangement makes the carbonyl group polar, which means the carbonyl has increased boiling and melting points.