1. G. W. Gray, Molecular Structure and the Properties of Liquid Crystals ( Academic Press, New York, 1962 ).
2. Several heterocyclic mesomorphic materials have been reported. See, for example, Reference 1, p. 157.
3. L. F. Trefilova and I. Y. Postovskii, Doklady Akad. Nauk S.S.S.R., 114, 116 (1957).
4. Reference 1, pp. 131–133.
5. We are indebted to Prof. G. W. Gray for providing his synthetic scheme.