Proton exchange in solutions of water in nitromethane and dioxane

The rates of proton exchange in the reaction H2O + D2O reversible arrow 2HDO have been studied in the solvents nitromethane and dioxane. For the solution in nitromethane to the upper limit of solubility of water (about 7 mol%) and in dioxane to a concentration of about 60 mol% the exchange remains rather slow. At higher concentrations the rate of exchange in dioxane increases rapidly with water concentration, indicating the promotion of the exchange via large water clusters. The isotope shift Deltadelta = delta(HDO) - delta(H2O) appears to be dependent on the concentration of water in the solvent, and an equation describing this dependence is proposed

Proton exchange in solutions of water in nitromethane and dioxane

The rates of proton exchange in the reaction H2O + D2O reversible arrow 2HDO have been studied in the solvents nitromethane and dioxane. For the solution in nitromethane to the upper limit of solubility of water (about 7 mol%) and in dioxane to a concentration of about 60 mol% the exchange remains rather slow. At higher concentrations the rate of exchange in dioxane increases rapidly with water concentration, indicating the promotion of the exchange via large water clusters. The isotope shift Deltadelta = delta(HDO) - delta(H2O) appears to be dependent on the concentration of water in the solvent, and an equation describing this dependence is proposed

Deuterium-induced carbon-13 isotope shifts in halogenomethanes

One-bond deuterium-induced carbon-13 isotope shifts in several chlorine, bromine and iodine derivatives of methane have been measured and used to construct a new incremental scheme for the calculation of carbon-13 isotope shifts in substituted derivatives of methane

The 18O/16O induced proton isotope shift in water

Measurements of proton NMR spectra at 750 MHz of dilute solutions of water in nitromethane reveals a small proton isotope shift due to 16O/18O substitution equal to about 1 ppb

Nonadditivity of D/H isotope effects on 13C chemical shifts in halomethanes

Nonadditivity in the values of the 13C isotope shifts for successive D/H replacements has been measured. The compounds studied are dichloromethane, dibromomethane, bromomethane and iodomethane. In all cases deviations from additivity, defined as the differences between the experimental isotope shifts and those obtained from the additive approach, were found to be negative (on the δ-scale) and to be of order 1-4 ppb. The nonadditivity may be explained using the approach proposed by Jameson and Osten and based on the idea of different secondary geometrical isotope effects produced by deuterium on the neighbouring CH and CD bond lengths. However, this approach requires unrealistically large difference in these secondary geometrical effects. An alternative approach based on recently calculated CH and CD bond displacements is proposed where nonadditivities may be attributed to small quadratic corrections to the secondary geometrical effects. © 1994

Deuterium-induced primary and secondary isotope effects on 13C,H coupling constants in halomethanes

Primary pΔJ(13C,H) and secondary sΔJ(13C,H) isotope effects on carbon-proton coupling constants were measured in studies of proton-and deuteron-coupled 13C NMR spectra of the halomethanes CHnDmX4-n-m, where X is Cl, Br or I. Both effects are always negative. The magnitudes of pΔJ(13C,H) increase with the number of halogen atoms whereas those of sΔJ(13C,H) decrease. pΔJ(13C,H) is almost linearly dependent on the number of halogen atoms whereas for sΔJ(13C,H) the dependence is non-linear. New results for the isotope effect on the 13C,H coupling constant in fluoroform are in accord with data for the other members of the haloform series. For CH3Br and CH3I estimates of the main features of the surfaces for the 13C,H coupling constants were made using known molecular force fields. © 1998 John Wiley & Sons, Ltd

ISOTOPE EFFECTS ON THE C-13 CHEMICAL-SHIFT AND CARBON-PROTON COUPLING-CONSTANT IN DICHLOROMETHANE

Carbon-proton and carbon-deuteron coupling constants were measured in the isotopomers CH2Cl2, CHDCl2, and CD2Cl2. The primary and secondary isotope effects on the carbon-proton coupling are -0.60 (+/- 0.05) and -0.25 (+/- 0.01) Hz, respectively. The deuterium-induced C-13 isotope shifts proved to be almost linearly dependent on the number of deuterium atoms, although there is a small but significant non-additivity

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 ⇌ 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. © 1999 Academic Press

Deuterium-induced primary and secondary isotope effects on 13C,H coupling constants in halomethanes

Primary pΔJ(13C,H) and secondary sΔJ(13C,H) isotope effects on carbon-proton coupling constants were measured in studies of proton-and deuteron-coupled 13C NMR spectra of the halomethanes CHnDmX4-n-m, where X is Cl, Br or I. Both effects are always negative. The magnitudes of pΔJ(13C,H) increase with the number of halogen atoms whereas those of sΔJ(13C,H) decrease. pΔJ(13C,H) is almost linearly dependent on the number of halogen atoms whereas for sΔJ(13C,H) the dependence is non-linear. New results for the isotope effect on the 13C,H coupling constant in fluoroform are in accord with data for the other members of the haloform series. For CH3Br and CH3I estimates of the main features of the surfaces for the 13C,H coupling constants were made using known molecular force fields. © 1998 John Wiley & Sons, Ltd

Deuterium-induced carbon-13 isotope shifts in halogenomethanes

One-bond deuterium-induced carbon-13 isotope shifts in several chlorine, bromine and iodine derivatives of methane have been measured and used to construct a new incremental scheme for the calculation of carbon-13 isotope shifts in substituted derivatives of methane