Abstract2D31P,15N heteronuclear shift correlation, based on a non‐refocused INEPT pulse sequence with15N detection, was applied to a15N NMR study of the azadiphosphiridines 1‐5 which are formed by [2 + 1] cycloaddition of iminophosphines, RPNR′. The pulse sequence used allowed consistent assignment of both the31P and15N NMR spectra in one experiment; by a slight modification, also the signs of numerous31P‐15N coupling constants across one or two bonds could be determined. Comparison of the data with those of the azatriphosphetidine 6 (obtained from ID1H,15N and31P,15N INEPT spectra) showed the influence of the ring size and conformational effects on the NMR parameters.31P,13C shift‐correlated 2D spectra were further used to measure (including sign determination) and assign31P‐13C coupling constants across one to three bonds in 1‐5. Based on the analysis of the coupling information and the known conformation of 4a, the relative stereochemistry of the diastereomers 4a and b could be derived; further, the comparison of the31P‐13C coupling data of 1‐3 with those of the 4a and b allowed the conformations of these derivatives, which were previously unknown, to be determined. The derived information of the constitution and stereochemistry of 1‐5 gives insight into mechanistic details of the iminophosphine