C-H⋅⋅⋅X-C bonds in alkyl halides drive reverse selectivities in confined spaces

Binding of non-activated alkyl halides (2–20) in water-soluble cavitand (1) through supramolecular forces is here reported, with emphasis on the role of size and polarizability of the halogen atom in the formation of intramolecular C-H hydrogen bonds in confined spaces. Rare reverse affinity in water (RI < RBr < RCl) is surprisingly observed for the more water-soluble short alkyl halides in dynamic open-ended containers. Competitive bindings and theoretical calculations confirm the unusual selectivity and the presence of C-H hydrogen bonds in non-activated systems for the first time, pointing out the importance and effect of subtle forces on molecular recognition in confined spaces.