Deuterium and carbon-13 NMR study of a banana mesogen: Molecular structure and order

The orientational order and the molecular structure of the banana mesogen 4-chloro-1,3-phenylene bis{4,4'-(11-undecenyloxy)benzoyloxy}benzoate have been studied in its nematic phase by means of H-2 and C-13 NMR. A detailed discussion of orientational order parameters for either the entire molecular core or the selectively deuterated fragments, and geometrical features concerning the rigid core of the molecule is given. In particular, the angles thetai between the para axis of the aromatic ring and the long molecular axis for each lateral wing are estimated. Quantum chemical calculations on the rigid core made by the central five aromatic rings, employing the B3LYP density functional method, support the molecular structure derived from the NMR results. This study shows how important is the comparison between H-2 and C-13 NMR to better understand the real structure of banana-shaped compounds in their mesophases and further sheds light on the open question about chirality or achirality of banana molecules.