Angular correlation and diamagnetic susceptibilities studied by high field NMR

Abstract

High field high resolution NMR has been used to determine the components of the magnetic susceptibility tensor and the angular correlation factors g2 for nitrobenzene, toluene, and benzene. For nitrobenzene an accurate concentration dependence study of the effective susceptibility anisotropy and asymmetry has been made. The angular correlation around the three principal molecular axes has been studied. For all compounds the g2 factor along the main molecular axis is in agreement with that found by the Cotton–Mouton effect and depolarized Rayleigh scattering studies. For nitrobenzene and toluene g2 cannot be interpreted in terms of simple monomer–dimer equilibria. For benzene a dimer model is shown to describe the liquid behavior satisfactorily.

Magnetic field-induced effects on NMR properties

“…In other words, dipole-dipole couplings, quadrupole couplings, and the anisotropies of spin-spin coupling and chemical shift affect the observables. Such effects were detected already in the mid-1980's for the 2 H quadrupole coupling in substituted benzenes, pyridine and aniline, 10,11 and for the 1 H- 13 C coupling in o-dichlorobenzene. 12 In 1995, the field-induced effect on the ortho 1 H-1 H coupling in benzene and halobenzenes was reported by Laatikainen et al 13 and, for the 15 N chemical shift in a protein-DNS complex, by Ottiger, Tjandra and Bax.…”

Lanthanide ion assisted magnetic alignment of model membranes and macromolecules

“…As such, an aggregate of N = 10,000 molecules (the approximate size of a bicelle) would be expected to yield a maximal quadrupolar splitting on the order of N × 1/15 B 2 / 0 kT × 0 75 × 168 kHz = 0 075 kHz at 11 75 T and 40 • C. However, as Fig. 1 suggests, bicelles would be expected to be packed at a sufficient density to significantly impair free tumbling of a given bicelle, leading to a cooperative aligning potential and much higher order parameters (33). Thus, very small magnetic anisotropies may lead to uniform alignment in liquid crystals, due to these long range (packing) interactions.…”

Dipolar Interactions in Molecules Aligned by Strong AC Electric Fields

“…The interaction can, however, be recovered if tumbling molecules are given preferential orientation. If molecules which possess large magnetic susceptibility anisotropies are oriented with strong magnetic fields (3)(4)(5), or if molecules are mechanically ordered by a liquid crystalline medium (6 -9), then the time average of the expression ( Electric fields can also be used to partially recover quadrupolar, dipolar, and chemical shift anisotropy interactions because they can introduce residual ordering in polar liquids. Thus, electric field NMR can provide an alternative tool for studying molecular structure.…”