Oxygen-17NMR spectra were obtained from the four pairs of isomeric 2-R-2-oxo-1,3,2-dioxaphosphorinanes, where R = OMe (2), NMe, (3), H (4) or Me (5). The isomerism has been previously shown to be confignrational at phosphorus, with one isomer of each pair having an equatorial phosphoryl oxygen (a isomer), and the other an axial orientation for phosphoryl oxygen (b isomer). Only data for the phosphoryl oxygen are reported. Substitution of OMe or NMe, for H or Me produced upfield shifts of 27.941.8ppm. In all cases, the chemical shifts of the a isomers were upfield of the b analogs, with difierences of 7.9, 18.0, 20.3 and 8.6ppm for 2-5, respectively. The absolute values of 1J(31Pi70) were 5-9Hz larger for the a isomers.