Multinuclear NMR Studies and Spin System Analyses on Dibenzo[c.e][1,2]Oxaphosphorine 2‐Oxides

2H‐Dibenzoc.e]1,2]oxaphosphorine 2‐oxide (HDOPO), 2‐(N,N‐diethylamino)‐dibenzoc.e]1,2]oxaphosphorine 2‐oxide (DEADOPO), and 2‐ethoxy‐dibenzoc.e]1,2]oxaphosphorine 2‐oxide (EtODOPO) are fully characterized in CDCl₃ by ¹H, ¹³C, ³¹P, and ¹⁵N NMR spectroscopy on 800‐ and 500‐MHz instruments. A strategy enabling their unambiguous signal assignment is presented, with special emphasis on 2D ¹H,¹³C HMBC spectra. Additional line‐shape iterations of the aromatic ¹H multiplets (ABCDX and ABCDEX spin systems) provided all long‐range ⁿJ_H,H and ⁿJ_P,H coupling constants with utmost precision. The experimental results augmented with those of the model compound phenylphosphonous acid clearly demonstrate that ⁿJ_H,H couplings of the PH proton as well as the ⁿJ_P,C values do not decrease in a monotonic manner with the number of intervening bonds from the phosphorus atom. This fact may potentially lead signal misassignments, if the analysis starts out from the coupling constants, as it occurred for HDOPO in the recent publication by Wagner et al. (Phosphorus, Sulfur and Silicon, 187, 2012, 781–798). The corrected assignment will be given in the present paper. Finally, the A₂M₃X or ABM₃X type ¹H spectral patterns of ethyl groups are also analyzed and explicit equations are derived to evaluate the strongly coupled ABM₃X multiplets in EtODOPO.