Attractive interactions between negative charges and polarizable aryl parts of host–guest systems

NMR measurements of associations between simple organic host and guest molecules bearing alternatively negatively charged groups and electroneutral π‐moieties show in aqueous solutions weak but distinct attractions reaching approximately 2 kJ mol−1 and X−/arene unit. A similar value is observed for the complex between a calixarene with 4‐sulfonato groups and toluene, for which the NMR shifts indicate an orientation with the guest methyl substituent upwards. The conformational fit of the selected complexes is checked by molecular mechanics simulations.