Journal of Physical Chemistry B, Vol.104, No.50, 12021-12027, 2000
Proton NMR study on selective hydration of anions in nitrobenzene
The selective hydration of univalent anions (X- = Cl-, Br-, I-, NO3-, ClO4-, SCN-) in deuterated nitrobenzene was studied by means of H-1 NMR spectroscopy. The dependence of the chemical shift of water protons upon water- and ion-concentrations clearly showed that the selective hydration to the anions can be elucidated in terms of the successive reaction mechanism: X-(H2O)(m-1) + H2O reversible arrow X-(H2O)(m) (m = 1, 2, 3,...). By curve-fitting analyses, the successive formation constants and the intrinsic chemical shifts could be evaluated for the hydrated anions in different hydration states. Spin-lattice relaxation times were also measured for various water- and ion-concentrations, and likewise analyzed on the basis of the successive reaction mechanism. The intrinsic rotational correlation times evaluated for the hydrated anions in different states were usually larger than similar to3 ps for free waters, suggesting the restriction of the rotational diffusion of water molecules by bonding with the anions.