The anisotropic coupling constants between unpaired electron spin and the nuclei can be determined from the ESR spectra of the nematic solutions. The spin Hamiltonian operator is of the same form for monoradicals in the two liquid solutions, but the values of the coupling constants change. The effective anisotropic coupling components are obtained from the coupling constants observed in nematic solutions by subtraction of the scalar coupling constants. The magnitudes of the scalar coupling constants can be reliably determined in the isotropic solution above the clear point.To calculate a degree of order from an experimentally determined anisotropic coupling component, the corresponding coupling tensor must be known, e.g. from theoretical studies or from independent measurements. As in the case of nuclear magnetic resonances, the sign of a scalar coupling can be determined if the preferred orientation is known. The results obtained for the tetracyanoethylene anion, for example, confirm the positive sign of the scalar coupling to the nitrogen [871. In the case of biradicals, the magnetic dipole-dipole interaction between the impaired electrons is no longer completely balanced out in nematic solutions. An additional coupling therefore occurs and this leads to the splitting of the resonance lines [**I.Glarum and Marshall "071 carried out particularly comprehensive studies on the perinaphthenyl radical. A comparison of the observed scalar and anisotropic coupling constants with calculated values showed good agreement. The g tensor was determined: g5 = g, = 2.00278 and gy := 2.00226 (< axis perpendicular to the plane of the molecule). gc is roughly equal to the g value of the free electron, ge = 2.00232. The planar radical is highly oriented in nematic liquid 4,4'-bis(methoxy)azoxybenzene. On average, the parallelism of the plane to the magnetic field is as good as that of the longitudinal axes of the solvent molecules. Fig. 2-4 I am grateful to

No abstract

No abstract

Abstract

No abstract