Hydrogen Bonding in a Host−Guest System: C-Undecylcalix[4]resorcinarene and Water in Benzene

The behavior of water in a benzene solution of C -undecylcalix[4]resorcinarene (UR) is studied by 1 H 2D NMR exchange spectroscopy and by 1D NMR. The rate constants for exchange of the UR hydroxyl protons, H a, with water over the temperature range 298−338 K are 0.7−4.6 s -1 and those for the exchange of UR hydroxyl protons, H b, over the temperature range 298−328 K are 1.8−8.1 s -1 . Activation energies calculated for these exchange processes are 9.0 ± 0.5 kcal/mol and 10.2 ± 1.0 kcal/mol, respectively. The chemical shift of dissolved water is largely dependent upon the concentration of UR. An upper limit for the critical aggregation concentration of UR is 10 -5 M as shown by 1 H NMR.