Aromatic ring dynamics in crystalline penicillins from variable temperature 13C cross-polarisation magic-angle-spinning n.m.r

A combination of lineshape analysis and magnetisation transfer experiments in variable temperature 13C cross-polarisation magic-angle-spinning n.m.r. spectroscopy has enabled the determination of rate and activation parameters for aromatic ring rotations over a motional frequency range of 10–2–106 Hz in crystalline penicillin derivatives.