Phosphorus-proton Spin-spin Coupling in the P–O–C–H Group. A Comparison of Cyclic and Acyclic Systems

Proton magnetic resonance spectra for eleven compounds with the POCH system have been examined. They are three 4-phenyl-2,2-disubstituted(X,Y)-1,3,2-dioxaphosphorinanes where X=Cl, Y=O (I); X=Cl, Y=S (II); and X=O−K+, Y=O (III); four 5,5-dimethyl-2,2-disubstituted (X,Y)-1,3,2-dioxaphosphorinanes where X=Cl, Y=O (IV); X=Br, Y=O (V); X=Cl, Y=S (VI); and X=OH, Y=O (VII); and four dimethyl phosphates, Y=P(-X)-(-OCH3)2, where X=Cl, Y=O (VIII); X=Br, Y=O (IX); X=Cl, Y=S(X); and X=O−12Ba2+, Y=O (XI). It has been found that the 1,3,2-dioxaphosphorinane ring in each of I–VIII is virtually fixed in a chair form in the solution, and there is no appreciable ring inversion as confirmed by NMR spectra. The phosphorus-proton coupling constant of the POCH system with the gauche relation (Jg) and that with the trans relation (Jt) were determined in each of these compounds (I–VII). The 23Jg+13Jt values calculated from the determined Jg and Jt values are always smaller than the 23Jg+13Jt values observed for the corresponding acyclic compounds (VIII–XI). This difference was explained in terms of a slight flattening of 1,3,2-dioxaphosphorinane ring from the ideal chair conformation.