Orientational order study of monolayers at the air–water interface by Maxwell-displacement current and optical second harmonic generation

A theoretical study of nuclear magnetic resonances in liquid crystals and in liquid crystalline solutions is given. The average ordering of the molecules in liquid crystals, as far as it is of importance for nuclear resonance researches, can be described by a symmetrical matrix. With the help of this matrix the coupling constants of the effective average spin HAMiLTONIAN can be expressed by the constants belonging to a fixed molecular orientation. For experimental work solutions in nematic liquid crystals are most useful. In such solutions high resolution spectra of the orientated solute molecules can be gained without any disturbance by intermolecular nuclear dipole-dipole interaction. Precise informations can be obtained on the intra-molecular dipole-dipole interaction, the anisotropy of chemical shift, and the quadrupole interaction. The matrix of order can be determined if the molecular structure is sufficiently known. In favorable cases the absolute sign of the indirect spin-spin coupling constants can also be determined.