Novel Mesogenic Benzoic Acids with Large Branches I. Synthesis, Liquid Crystalline Properties and Crystal Structure Analyses of 3-(4-Subst.-benzyloxycarbonyl)-4-(4-n-octyloxybenzoyloxy) benzoic Acids

Abstract

New benzoyloxybenzoic acids bearing both terminal and lateral groups have been synthesized. Substituted aryl rings are laterally attached to the basic mesogens by means of an odd-numbered spacer. Therefore, liquid crystalline behaviour can be observed at high temperatures.

The crystal and molecular structure of 3-(4-cyano-benzyloxycarbonyl)-4-(4-n-octyloxybenzoyloxy)benzoic acid 3b has been determined by X-ray analysis. 3b crystallizes in space group P2_1/n with four molecules in a unit cell of the following dimensions: a = 15.682(2), b = 7.701(1), c = 23.107(3)Å β = 97.69(1)°. The structure was solved by direct methods and refined to an R value of 0.057 for 3684 observed reflections.

The molecules of 3b are associated to dimers with a shape unusual for mesogens exhibiting nematic and smectic phases. In the crystal the dimers are closely packed to ribbons which on their part are connected to lamellar sheets. The nitro-substituted homologue 3c was proved to be isostructural with 3b.

Key Words:

• Liquid crystalline benzoic acids
• bulky branched mesogens
• molecular structure
• crystal structure
• hydrogen-bonded dimers