End-chain ordering and even-odd effects in nematic thermotropic liquid crystalline mesophases studied by deuterium magnetic resonance

Abstract Deuterium quadrupole splittings are reported for the nematic mesophases of all isomers of 4,4′-di- n -octyl- d 4 ( d 6 )-oxyazoxybenzene with CD 2 (CD 3 ) groups at corresponding segments in the two end chains. These splittings do not decrease monotonically with increasing separation of the chain segment from the aromatic core as has previously been assumed. Comparison with similar measurements for 4,4′-di- n -heptyloxyazoxybenzene reveals an “even—odd” effect in the chain ordering, but only in so far as to reflect differences in the molecular order in the two mesophases. The results are used to test earlier theoretical calculations by Marcelja.