Steric Structure of Phosphorus Containing Heterocycles Xlv. Spectral¹h And¹³c NMR Criteria for Conformational Studies of 1,3,2-Dioxaphosphocines

The 13C and dynamic 1H NMR spectroscopy were employed to derive spectral tests for conformational studies of eight-membered phosphorus (PIII and PIV) containing heterocycles: 4,5; 7,8-dibenzo-(I) and dinaphto-(II) 1,3,2-dioxaphosphocines. Passing from series (I) to (II) causes a dramatic change in the shift difference of methylene protons at C-6. The geminal 2 J(HH) and long-range 5 J(PH) spin-spin couplings are determined by the ring structure. The latter is also influenced by the phosphorus valence state and the orientation of substituents at phosphorus. Fairly definite stereo-chemical assignments can be made using the n J(31P13C) couplings with n of 2 to 5.