Direct observation of the effects of small-amplitude motions on 13C nuclear shielding tensors by means of low-temperature 2D MAS NMR spectroscopy

Highlights: • Chemical shielding tensors (CST) at high-temperatures depend on vibrational motions. • Vibration amplitudes can be estimated by variable-temperature CST measurements. • Effects of vibrations are fundamental to compare experimental and calculated CST. • Vibrations are studied on multi-carbon molecules by low-T 2D-PASS experiments. Fast small-amplitude motions, such as vibrations or librations, do affect NMR properties of molecules in the solid state. The quantification of these effects is very important for structural studies exploiting Solid State NMR and computational methods, particularly in the field of NMR crystallography. In this work 2D MAS NMR experiments were carried out over a wide range of low temperatures (129–295 K) on a non-standard high-resolution Solid State NMR equipment to obtain the first experimental determination of the effects of small-amplitude motions on ¹³C Chemical Shift Tensors of a multi-carbon molecule (ibuprofen).