Effect of terminal branching on mesomorphism

Two new mesogenic homologous series having following general structural for mula have been synthesized. In series-I, n-octyloxy and n-dodecyloxy derivatives exhibit enantiotropic smectic A phase whereas n-decyloxy and n-tetradecyloxy derivatives exhibit monotropic smectic A phase, rest of the members are non-mesogenic. Looking to the terminally branched alkyl group smectogenic tendency of series-I is quite interesting. [GRAPHICS] Where n = 1 to 8, 10, 12, 14 & 16. Series X I - II [GRAPHICS] In series-II. all the members exhibit enantiotropic nematic phase. The smec tic C mesophase commences from the n-heptyloxy derivative and is exhibited along with nematic phase till the last n-hexadecyloxy derivative studied. T hough branching is known to be less conducive to mesomorphism, it is observ ed that entire series-II is mesomorphic in nature.