NMR study of 2-alkoxy-1,3,2-dioxaphospholanes. II—molecular conformation of alkoxy substituents

The conformation of some 2-σ-1,3,2-dioxaphospholanes (σ=OAlkyl, CI) is studied. The determination of the ²J(POC) and ³J(POCC) coupling constants, which are influenced by the bulk of the alkoxy group, is a means of obtaining information about the rotation around the P? OR bond, which is dependent on steric interactions between the phosphorus lone pair, the alkoxy group and the substituents on the ring. When σ is a tert-butoxy group, a direct ‘through-space’ interaction is found between the phosphorus atom and one of the primary carbons of the OR group. If there is no substituent on the ring, the ³¹P chemical shifts are little affected by changes in OR; a diamagnetic effect is observed, however, in the case of the tert-butoxy group which is enhanced for the 4,4,5,5-tetramethyl derivatives.