Three new series of heterocyclic pyrazoles Mpz-Cn and Epz-C n and isoxazoles Iz-Cn were prepared, characterized, and their mesomorphic properties investigated. These heterocyclic derivatives were obtained by condensationecyclization of β-diketones with methylhydrazine, 2-hydradinoethanol or hydroxylamine in refluxing THF/ethanol. One single crystallographic structure of nonmesogenic Epz-C4 was determined by Xřay analysis. It crystallizes in a triclinic space group P-1. An H-bond-induced structure was formed, giving a better aspect ratio required for the formation of mesophases. Both series of pyrazoles Mpz-Cn and EpZ-Cn exhibited monotropic smectic A phases, in contrast, isoxazoles Iz-Cn formed enantiotropic smectic C phases. A lack of H-bond due to a removal of hydrogen atom from pyrazolyl rings (-NH) significantly lowered the clearing temperatures of both Mpz-Cn and EpZ-Cn. These compounds have good thermal stabilities.
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Sheu, H. (Contributor), Kuo, H. (Contributor), Lai, C. K. (Contributor), Lee, G. (Contributor) & Tsai, S. (Contributor), The Cambridge Structural Database, 14 Jan 2013