Absolute signs of the order parameters and the structures of benzo[C]bisisothiazoles

Abstract

Proton NMR spectra including the 13C-satellites of two benzobisisothiazoles, namely, benzo (1,2-C : 4,3-C')- and benzo (2,1-C : 3,4-C')bisisothiazoles (referred to as (I) and (II) repsectively) have been studied in the nematic phase of N-(P'-ethoxyben-zylidene)-p-n-butylaniline. The derived HH and 13CH direct dipolar couplings have been corrected for harmonic vibrations and the ragr structures derived. The results indicate that the molecules are planar and there is a considerable bond fixation in (II). As some of the dipolar couplings could not be derived precisely in (I), it was hard to conclude anything definite about the bond fixation.

In (I) the magnitude of the order parameter of the axis perpendicular to the C2-symmetry axis and in the molecular plane is larger than 0.5 and hence its absolute sign is positive. In analogy with (I), the signs of the order parameters in (II) have also been derived.