Synthesis of liquid crystals—strategies and methods

The previous chapters have shown how and why the mesomorphic properties and the other physical properties of liquid crystals vary so enormously with the various stmctiual moieties and their particular combinations. However, of great importance to the progress of the hquid crystal field is how the particular structural moieties are irrtroduced in the reqtrired combirrations to provide materials that generate hqirid crystalline phases. In this chapter the strategies of liqirid crystal synthesis are discussed and some of the scope and limitatiorrs of the synthetic methods used are cortsidered. 

The synthetic rentes considered do not necessarily represent those originally used in the preparation of liqnid crystal materials, becanse mat r advances have been made since the early days of snch syntheses. 

Traditionally, liquid crystals based on aromatic cote rrrrits are the most common because of the relative ease of syrrlhesis. 

Many functionalised aromatic units are commercially available or reasonably easy to synthesize directly through electrophilic substitution reactions (e.g., Friedel-Crafts acylation, bromination and nitration) subsequent functional group interconversions allow access to those groups that carmot be directly introduced (e.g., -CO H, -NH2, -CN and 

Plate 1 Schlieren texture of the nematic liquid crystal phase. 

---

Synthesis of Liquid Crystals—Strategies and Methods 179 Pd(PPh3)4, /r /=, ... 

This brief account of methods for the synthesis of nematic liquid crystals concentrates on the most frequently encountered core systems, linking and terminal groups the synthetic methods presented are often applicable to more unusual nematogens and to compounds showing other mesophases (see V. Vill in Volume 1, Chapter IV on General Synthetic Strategies). 

---