In
chemistry, a
leaving group is a molecular fragment that departs with a pair of
electrons in
heterolytic bond cleavage. Leaving groups can be
anions or neutral molecules, but in either case it is crucial that the leaving group be able to stabilize the additional electron density that results from bond heterolysis. Common anionic leaving groups are
halides such as Cl
-, Br
-, and I
-, and
sulfonate esters such as
tosylate (TsO
-). Fluoride (F
-) functions as a leaving group in the nerve-agent
sarin gas. Common neutral molecule leaving groups are
water and
ammonia.