“near Magic Angle” Sample Spinning in Nmr Spectra of Molecules Oriented in Individual and Mixed Liquid Crystals of opposite Diamagnetic Anisotropies

The dynamics of the liquid crystal director in “near magic angle” sample spinning has been investigated in mesophases with positive and negative diamagnetic susceptibility anisotropies and their mixtures with near-zero macroscopic diamagnetic anisotropy. To this end the deuteron quadrupolar splitting of deuterochloroform dissolved in liquid crystals has been monitored. In systems with weakly positive diamagnetic susceptibility anisotropy (Ax), the director has been observed to switch from an orientation parallel to the spinning axis at low rotational speeds to one perpendicular to the spinning axis at high rotational speeds when the angle (6) the axis of rotation makes with the magnetic field is smaller than the magic angle (0,). For systems with a small negative Ax similar director behaviour has been observed for 13 greater than B,,,.