Peak doubling in the nuclear magnetic resonance spectra of certain phosphorus esters

Doubling of nuclear magnetic resonances of certain mixed phosphorus esters has been observed and has been attributed to the presence of rotational conformers occupying "up" and "down" orientations of the ester moieties. Treatment of these esters with uranyl nitrate results in the expected resonances, although chemically shifted.This is believed to be due to the "freezing" of rotational conformers by complex formation. Dependence of the observed resonances upon temperature supports this hypothesis. There appears to be some steric control over the relative population of the contributing conformers.