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Resonances from carbons bonded to nitrogen are often broadened and split into asymmetric doublets in 13C NMR spectra of polycrystalline organic molecules obtained with proton decoupling and magic-angle sample spinning.

The dipolar coupling between 14N and 13C is not suppressed by magic angle sample spinning because the relatively large 14N quadrupole interaction shifts the axis of quantization of the 14N spins away from the direction of the applied field. The resulting 13C resonance line shapes are influenced by the sign, magnitude, and asymmetry parameter of the 14N quadrupole coupling tensor; the internuclear distance; the magnitude of the applied magnetic field; and the orientation of the internuclear vector in the principal axis system of the electric field gradient. It is demonstrated that one or more of these parameters can be determined from the 13C NMR data if the others are known by virtue of single crystal studies or molecular symmetry.