Dipolar Dephasing as an Assignment Tool

The dipolar dephasing sequence is routinely used in ¹³C CPMAS NMR as described previously. The lower trace of the figure below is the ¹³C CPMAS spectrum of Dianin's compound which forms an inclusion compound with ethanol. The upper trace shows the ¹³C CPMAS spectrum with a 40 microsecond dephasing delay. All rigid CH and CH₂ carbon signals disappear leaving the quaternary carbons. The methyl signals and the CH₂ signal for ethanol survive the delay as the carbon - proton dipolar coupling is very much reduced due to methyl group rotation and molecular motion of the ethanol, respectively.