Hindered rotation of CH3 groups and phenyl ring in clofibric acid (drug) studied by35Cl-NQR and1H-NMR spectroscopy

The35C1-NQR frequency (VQ), nuclear quadrupole spin-lattice relaxation time (T1Q),1H-NMR second moment (M 2), nuclear magnetic spin-lattice relaxation time (T 1) and spin-lattice relaxation time in rotating frame (T 1p ) were measured for polycrystalline clofibric acid (drug) as a function of temperature. Hindered rotation of two dynamically inequivalent methyl groups and the phenyl ring was detected, the relevant activation energies were determined. The rotations are discussed in detail.