Abstract
The cholesteryl esters (3b and 3a) of 5-carboxy-1,3-phenylene-16-crown-5 and 5-carboxy-4,6-dichloro-1,3-phenylene-16-crown-5 show cholesteric liquid crystalline behavior but only upon heating samples that were rapidly cooled from the isotropic melt in the case of 3a and a monotropic phase for 3b. The dichloro compound 3a was formed by treatment of the corresponding acid 2 with SOCl2 first and then cholesterol; it is believed that the SOCl2 was contaminated with SO2Cl2, leading to the chlorination of the aromatic ring. The dichloro compound 3a was structurally characterized using single crystal X-ray diffraction. 3a crystallizes in the orthorhombic space group P212121 with unit cell parameters of a = 12.76(4) A, b = 17.511(5) A, and c = 18.213 A. Use of freshly opened SOCl2 produced 3b. The reaction of the acid 2 and cholesterol in the presence of dicyclohexylcarbodiimide yielded the acylisourea 4 as the major product (64%) along with 3b (36%) upon treatment with cholesterol. The dicholesteryl ester 9 of b...
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