Syntheses of Standard Smectic Liquid Crystals

In the following sections, by way of example, the syntheses of standard and much investigated smectic liquid crystals will be described. These syntheses will give a general perspective on the synthesis of smectic liquid crystals from basic starting materials. 

1 Synthesis of 4-Alkyl-and 4-alkoxy-4 -cyanobiphenyls Interdigitated Smectic A Materials (e.g., 8CB and (80CB) 

The alkoxy analogue can be prepared in a variety of ways, one route involves the bromination of protected hydroxybiphenyl, subsequent deprotection and alkylation which results in the creation of the alkoxy bromobiphenyl, see the left-hand side of Fig. 28. Cyanation using copper(I) cyanide as above yields the final product. Alternatively, the alkoxy cyanobiphenyls can be prepared by a cross-coupling procedure as shown on the right-hand side of Fig. 28. Selective coupling of 4-iodo-bromobenzene with an alkoxyphenyl boronic acid in the presence of palladium(O) yields the alkoxy bromobiphenyl. Cynanation proceeds as described previously. 

This second example provides a comparison between two different synthetic strategies. One method uses a pathway that maintains the integrity of the core throughout, whereas the other, newer, method builds the core up with the substituents already attached and in place. This second technique is very powerful when complex core structures are required or where lateral substitution in the core is difficult to achieve using conventional electrophilic substitution techniques [39], 

2 Synthesis of Alkyl 4-Alkoxybiphenyl-4 -carboxylates Hexatic Smectic B Materials (e.g., 650BC) 

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