Cyclic organophosphorus compounds. Part VIII. Conformation in the 1,3,2-dioxaphosph(V)orinan series. Proton magnetic resonance assignments to gem-5,5-dimethyl groups, and conformation at phosphorus

Chemical shifts for the gem-dimethyl groups in 5,5-dimethyl-1,3,2-dioxaphosph(V) orinans are reported for solutions in deuteriochloroform and benzene. Strong coupling between axial 4(6)-protons and the axial 5-methyl group is evident, and decoupling experiments further suggest that 5JPH is negligible or at least non-specific. For chloroform solutions of aralkyl phosphonates preferential shielding of the axial methyl group suggests that the aralkyl group and the phosphoryl bond lie in the equatorial and axial positions respectively.