Proton, carbon, and phosphorus nuclear magnetic resonance and conformational studies on phosphate esters

The conformational free energies of phosphate and phosphoryloxymethyl groups on a cyclohexane ring were 0.94 and 0.88 kcal mol–1 in deuterium oxide at pD 5 and 0.20 and 1.09 kcal mol–1 in 2H6dimethyl sulphoxide, respectively. For the rotational isomerism of the C–O axis of phosphate esters, 3JPH coupling constants indicate that the conformers with a planar trans arrangement of P–O and C(1)-CH2 bonds on primary phosphates or of P–O and C(1)–C(2 or 6) bonds on secondary phosphates predominated. The carbon magnetic shieldings in the vicinity of the phosphate ester function are interpreted in terms of an electronic exchange process.