This article presents a detailed discussion on medium effect oil ionic S(N)2 reactions. Ion pairing and the first solvation shell play the main role oil reactivity. Ab initio calculations are used to show that a combination of apolar molecular cavity with polar hydroxyl groups can have catalytic effects oil these reactions. The present results open ail avenue of development for supramolecular catalysts able to control bimolecular ionic reactions. In particular, this new catalytic concept could be useful in nucleophilic fluorinations.