Acyclic compounds 5 and 6 were prepared to investigate the difference in the anion binding ability of the encapsulated and preorganised binding cavity of the macrocyclic tetralactam scaffold compared to its acyclic components. Compounds 5 and 6 correspond to the two acyclic halves of macrocycle 2a. The Cl -binding constants of both 5 and 6 were very low at Ka = 16 and 12 M -1 , respectively (Table ). Comparing the low binding constants of 5 and 6 to the binding constant achieved by tetralactam 2a of Ka = 545 M -1 highlights the benefits of binding site preorganisation (Table ).