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Abstract
Three homologous series of α,α′-Dimethylbenzalazines, have been synthesized: 4,4′-Dialkoxy-α,α′-Dimethylbenzalazines, 4,4′-dialkoxy-2,2′-dihydroxy-α,α′-Dimethylbenzalazines, and 4,4′-dialkoxy-2-hydroxy-α,α′-Dimethylbenzalazines. The influence of molecular structure on the mesomorphic properties was studied.
Mesomorphic properties and phase transitions were determined using a polarizing hotstage microscope and a differential scanning calorimeter. The introduction of one or two hydroxyl groups in position 2- or 2-and 2′- of the aromatic rings (4,4′-dialkoxy-2-hydroxy-α,α′-Dimethylbenzalazines and 4,4′-dialkoxy-2,2′-dihydroxy-α,α′-Dimethylbenzalazines respectively) gives molecules with an excellent mesogenic quality, and all the prepared compounds of these series exhibit mesomorphism. Compounds of the series with two hydroxyl groups exhibit smectic polymorphism which is not so in the case of the compounds of the other series. The melting temperatures are systematically lower for the 4,4′-dialkoxy-2-hydroxy-α,α′-Dimethylbenzalazines than for the other two series.