HYDRATION OF AMINES, DIAMINES, POLYAMINES AND AMIDES STUDIED BY NMR

The spin-lattice relaxation times, T-1, of natural abundance (H2O)-O-1 7 have been measured for aqueous solutions of nine amines, five diamin es, two polyamines and five amides, as a function of the concentration at 25 degrees C. The water-accessible surface areas of the solute mol ecules were calculated. The coordination number, n(h), and the rotatio nal correlation times, tau(c)(0), of water molecules around the solute molecules were estimated and compared with that of pure water tau(c)( 0). The value of tau(c)(h)/tau(c)(0) = 2.02 for tert-butylamine is the largest and that of tau(c)(h)/tau(c)(0) = 0.97 for urea the smallest obtained. The value of n(h) (tau(c)(h)/tau(c)(0)-1) was defined as the dynamic hydration number (DHN). The partial molar volumes and the par tial molar heat capacities for these homologues at infinite dilution a re linearly dependent on their DHN.