The behavior of water in;a benzene solution of C-undecylcalix[4]resorcinarene (UR) is studied by H-1 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, Hb, 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 H-1 NMR.