Abstract: The crystal and molecular structures of the mesogenic 2,5-bis-(4-ethylbenzoyl) oxystyrene(Ⅰ) and 2,5-bis(4-methoxybenzoyl) oxybenzaldehyde (Ⅱ) have been determined by single crystal X-ray diffraction methods. Both compound Ⅰ and compound Ⅱ are liquid crystalline.
Crystal data:
Compound Ⅰ, C_2H_5·C_6H_4·COO·C_6H_3(CH:CH_2)·OOC·C_6H_4·C_2H_5, triclinic, space group P(1) (No.2), a=0.9356(6), b=0.9842(6), c=1.3357(8) nm, α=108.68(5)°, β=105.67(5)°, γ=96.36(5)°, Z=2; Compound Ⅱ, H_3CO·C_6H_4·COO·C_6H_3(CHO)·OOC·C_6H_4·OCH_3, monoclinic, space group Pn (No.7), a=0.9109(2), b=0.9187(3), c=2.3166(8) nm, β=93.93(2)°, Z=2.
In both crystals, the molecules take fully extended form with the long molecular axes of 2.27 nm for compound I and of 2.22 nm for compound II. The molecules of these two compounds are not plate-like but rather rod-like. The middle phenyl rings of the molecules rotate from the other two phenyl rings by 86.3° and 135.8 for compound I; and by 84.9° and 84.7° for compound II. All molecules are arranged parallel along their long axes in the crystals.
Compound I is a polymerizalbe monomer, it easily forms high molecular weight polymer upon heating without any initiators at about 140 ℃. Its high polymerizability might be explained by the fact that the molecules are packed such that the lateral vinyl groups of neighbouring molecules are closely correlated with a distance of only 0.47 nm and the energy-favorable parallel molecular arrangement, which is similar to the arrangment of the mesogens in its polymer.

Key words: Liquid crystal compound with laterally substituted mesogen, Crystal and molecular structure