Long-lived nuclear spin states in rapidly rotating CH 2 D groups.

Although monodeuterated methyl groups support proton long-lived states, hindering of the methyl rotation limits the singlet relaxation time. We demonstrate an experimental case in which the rapid rotation of the CH2 D group extends the singlet lifetime but does not quench the chemical shift difference between the CH2 D protons, induced by the chiral environment. Proton singlet order is accessed using Spin-Lock Induced Crossing (SLIC) experiments, showing that the singlet relaxation time TS is over 2min, exceeding the longitudinal relaxation time T1 by a factor of more than 10. This result shows that proton singlet states may be accessible and long-lived in rapidly rotating CH2 D groups.