Compound 2 is characterized by two non equivalent couples of stacked naphtyl moieties whose flipping is regulated by torsions around two carbon-carbon sp 3 bonds connected in one case to amide and in the other case to methylene moieties (see Figure ). Because of the bulky naphtyl sides, torsional barriers for the switching between conformers are in the case of compound 2 much higher than they are in compound 1 with phenyl groups, hence giving rise to long-lived metastable conformational states determining the conformational selectivity of this host molecule.