High Quality Content by WIKIPEDIA articles! A nucleofuge (derived from nucleo, nucleus, the positive part in an atom and fuge, fugetive, to run away, to escape) is a leaving group which retains the lone pair from its previous bond with another species. For example, in the SN2 mechanism a nucleophile attacks an organic compound containing the nucleofuge (the bromo group) which simultaneously breaks the bond with the nucleofuge.