Illustrated Glossary of Organic Chemistry

Functional group: A group of atoms whose bonding is the same from molecule to molecule. A functional group has similar behavior regardless of the molecule that contains it, so molecules with identical functional groups tend to have similar chemical and physical properties. In addition, functional groups with similar structures tend to impart similar chemical and physical properties to the molecules which contain them.

Common Functional Groups
  - means 'attached atom does not matter'      * means carbon or hydrogen here

Alkene	Alkyne	Benzene ring
Alkyl halide X = F, Cl, Br, or I Also called haloalkane	Alcohol	Phenol
Ether	Thiol Also called mercaptan	Sulfide Also called thioether
Disulfide	Amine	Ketone
Aldehyde	Carboxylic acid Often abbreviated RCOOH	Ester Often abbreviated RCOOR or RCO2R
Amide	Acid chloride Also called acyl chloride	Acid anhydride Also called anhydride
Carboxylate Also called carboxylate ion	Imine Also called Schiff base	Nitrile
	Nitro