Ultrahigh-resolution phosphorus-31 NMR

The feasibility of ultrahigh-resolution {sup 31}P NMR on both 200- and 500-MHz ({sup 1}H resonance frequency) instruments is demonstrated. Results indicate that temperature gradients within the sample caused by proton decoupling have severely limited the resolution achieved on commercial instruments due to the larger temperature dependence of {sup 31}P chemical shifts exhibited by many phosphorous-containing molecules, relative to {sup 13}C chemical shifts. Conditions are described under which instrumental contributions to the observed line width of as little as 15 MHz are observed. Measurements of {sup 31}P-{sup 13}C scalar coupling constants and {sup 13}C isotope effects on {sup 31}P chemical shifts are presented.