AbstractBy Fourier transform high resolution NMR spectroscopy the 31P signals of the phosphate species 31P16O4-n18On3- (n = 0, 1, 2, 3, 4) have been resolved in aqueous solutions of potassium phosphate. An isotope effect on the Larmor frequency of δ(31P) = (0.019 ± 0.002) to lower frequency was found for the substitution of a 18O atom for a 16O atom in the phosphate ion.
The 13C-carboxyl kinetic isotope effect on decarboxylation of 4-methoxyanthranilic acid has been determined in aqueous solutions of ionic strength 0.50 at 60 °C. The isotope effect, 100(k12/k13 −1), is found to be 4.2% at pH −0.3, 1.4% at pH 1.3, and zero at pH 4.0. This information makes it possible to decide between two mechanisms previously proposed in favor of the one in which both anion and neutral acid are protonated at carbon-1 of the aromatic ring but only the protonated anion decarboxylates.
The 13C NMR spectra of the bromide of the protonated iminophosphorane -substituted sponge 7 were recorded at different fields. Together with the use of 13C satellites of the 31P NMR spectrum, these experiments allow determination of a reasonable set of chemical shifts and coupling constants. The most interesting are a 4h JPP = 1.6 Hz, determined directly from the 31P NMR spectrum, which probably involves the hydrogen bond, and a 2Δ31P(13C) isotope shift of 9 ppb.
An Experimental Study of the 4hJ(31P–31P) Coupling Constant and the 12C/13C Isotope Effect on 31P in an Iminophosphorane-Substituted Proton Sponge