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ABSTRACT
Four liquid crystal compounds of the form 2-sec-butyl-4-[(4-X-phenyl) diazenyl) phenyl-4-(octadecyloxy] benzoate symbolized as I18a, I18b, I18c, and I18d were prepared in which the substituent (X) was taken CH3O-, CH3-, Br-, and -NO2, respectively. Characterization of prepared compounds is done using FT-IR, 1H-NMR, mass spectroscopy, and elemental analysis. Their mesophase was investigated by differential scanning calorimetry. Their antioxidant efficiency for Egyptian lubricating base oil was tested via monitoring the oxidation reaction through the change in total acid number. The obtained results showed that the efficiency of these compounds was ranked as follows I18d > I18c > I18b > I18a.