Structural characterizations using XRD and (13)C NMR spectroscopy of two rodlike mesogens consisting of (i) three phenyl ring core with a polar cyano terminal and (ii) four phenyl ring core with flexible dodecyl terminal chain are presented. The three-ring-core mesogen with cyano terminal exhibits enantiotropic smectic A phase while the four-ring mesogen reveals polymesomorphism and shows enantiotropic nematic, smectic C, and tilted hexatic phases. The molecular organization in the three-ring mesogen is found to be partial bilayer smectic Ad type, and the interdigitation of the molecules in the neighboring layers is attributed to the presence of the polar terminal group. For the four-ring mesogen, the XRD results confirm the existence of the smectic C and the tilted hexatic mesophases. A thermal variation of the layer spacing across the smectic C phase followed by a discrete jump at the transition to the tilted hexatic phase is also observed. The tilt angles have been estimated to be about 45° in the smectic C phase and about 40° in tilted hexatic phase. (13)C NMR results indicate that in the mesophase the molecules are aligned parallel to the magnetic field. From the (13)C-(1)H dipolar couplings determined from the 2D experiments, the overall order parameter for the three-ring mesogen in its smectic A phase has been estimated to be 0.72 while values ranging from 0.88 to 0.44 have been obtained for the four-ring mesogen as it passes from the tilted hexatic to the nematic phase. The orientations of the different rings of the core unit with respect to each other and also with respect to the long axis of the molecule have also been obtained.

KALLURU S. REDDY and PULIGUNDLA R. NAIDU. Can. J. Chem. 55.76 (1977). Excess volume data for mixtures of 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol with methylethylketone were determined at 303.15 and 313.15 K . These volumes are negative with 1-propanol and increasingly positive with the higher homologs, suggesting that the structuremaking effect of the ketone outweighs the structure-breaking effect in the first mixture of the series while the structure-breaking effect dominates in the other three mixtures. Further, the temperature coefficient of V E was found to be positive in all four mixtures. KALLURU S. REDDY et PULIGUNDLA R. NAIDU. Can. J. Chem. 55,76 (1977). On a determine, a 303.15 et a 31 3.15 K , les donnees concernant les volumes d'exces pour des n~ilanges de propanol-1, de butanol-1, de pentanol-1 et d'hexanol-1 avec la butanone-2. Ces volumes qui sont negatifs avec le propanol-1 augmentent d'une f a~o n algebrique lorsque I'on passe aux homologues superieurs; ces resultats suggerent que I'effet de formation de structure de la cetone contrebalance l'effet de brisure de structure dans le premier melange dela striealors que l'effet de brisure de structure domine dans les trois autres melanges. De plus on a trouve que le coefficient de temperature de V E est positif dans les quatre melanges.[Traduit par le journal]

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