STUDY OF ORIENTATIONAL ORDERING OF LATERALLY ALKOXY BRANCHED NEMATICSBY ONE AND 2-DIMENSIONAL C-13 NMR

The orientational ordering of the chains in three laterally substitute d compounds in the homologous series (4-(3'-n-alkoxy-4'-methoxybenzoyl oxy)salicylidene) aniline was investigated by one and two dimensional C-13 NMR. The C-13 chemical shifts were determined with slow spinning of the sample parallel to the magnetic field. When the sample is coole d from isotropic to nematic, a positive chemical shift is observed for the first methylene carbon in the lateral chain and for the methoxy g roup, while the chemical shifts of the other methylene carbons and the terminal methyl carbons change in the opposite direction. This indica tes that the mean chain conformation is not fully trans. Furthermore, the order parameters of the carbon in the chains obtained from 2D C-13 NMR with variable angle spinning show that the lateral alkoxy chain i s less ordered than the terminal n-butyl chain.