Isotope Effects on the 17O, 1H Coupling Constant and the 17O-{1H} Nuclear Overhauser Effect in Water.

The NMR spectra of solutions of 30% 17O-enriched H2O and D2O in nitromethane display the resonances of the three isotopomers H2O, HDO, and D2O. All 17O, 1H and 17O, 2H coupling constants and the primary and secondary isotope effects on J(17O, 1H) have been determined. The primary effect is -1.0 +/- 0.2 Hz and the secondary effect is -0.07 +/- 0.04 Hz. Using integrated intensities in the 17O NMR spectra, the equilibrium constant for the reaction H2O + D2O right harpoon over left harpoon 2HDO is found to be 3.68 +/- 0.2 at 343 K. From the relative integrated intensities of proton-coupled and -decoupled spectra the 17O-{1H} NOE is estimated for the first time, resulting in values of 0.908 and 0.945 for H2O and HDO, respectively. This means that dipole-dipole interactions contribute about 2.5% to the overall 17O relaxation rate in H2O dissolved in nitromethane. Copyright 1999 Academic Press.