Nuclear Spin Coupling and Conformation of the P–O–C–H Group

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Abstract
Proton magnetic resonance spectra have been observed of eight phosphoric acid esters in heavy water solutions. Among these esters, 1-phenyltrimethylene phosphate (1-phenyl-1, 3-propanediol cyclic phosphate) is a new compound. It was shown that the six-membered ring in this compound is fixed in a conformation at room temperature. On assuming that it is a chair form, 1-proton should be on the axial bond and this should be in a gauche relation with respect to the O–P bond around the C1–O1 bond. The proton-phosphorus coupling constant, JHp, in this H-C1–O1–P system was found to be 1.5 cps. The JHp in the CH3OP system was found to be 10.3–10.5 cps, and, therefore, JHp in the trans form is considered to be much greater (∼28.2cps) than that in the gauche form. The JHp the RCH2OP systems were found to be 6.3–7.0 cps, and, therefore, C–R bond in these systems are considered to have a greater chance of taking trans position with respect to the O–P bond around the C–O bond than the chance of taking gauche position.