H-2 NMR-SPECTRA OF -(P-HEPTYLBENZOYLOXY)-5-(P-HEPTYLBENZENAZO)TROPONE- A NEW SIGMATROPIC LIQUID-CRYSTAL

Liquid crystals incorporating in their molecular framework a seven-mem bered ring are still relatively rare [1]. Recently the synthesis and t hermal behaviour of a series of liquid crystal materials having a trop one moiety in their mesogenic core have been reported [2-4]. These mes ogens, based on a 2-(acyloxy)tropone core structure, show intramolecul ar migration of the acyl substituents between the two oxygen atoms at C-1 and C-2, an effect already known for simple 2-(acyloxy)tropones in their isotropic solutions [5]. This migration involves a concerted [1 ,9]-sigmatropic rearrangement [2]. This rearrangement could play a maj or role in determining the properties of the mesophases: it has been s uggested in fact that, because of this rearrangement, the mesogenic mo lecules acquire a mean rod-like shape which can sustain the mesophase formation [2]. In order to study the influence of the acyl migration o n the liquid crystalline properties of the tropone class of liquid cry stals, specifically from the point of view of the molecular orientatio nal ordering, we have synthesized both -(p-heptylbenzoyloxy)-5-(p-hept ylbenzenazo)tropone (1) and its partially deuteriated analogue 2: