Browsing by Author "LEU, YJ"

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PHOTOCYCLOADDITION OF FUMARONITRILE TO ADAMANTAN-2-ONES AND MODIFICATION OF FACE SELECTIVITY BY INCLUSION IN BETA-CYCLODEXTRIN AND ITS DERIVATIVES
(1995-02-01)
CHUNG, WS
;
WANG, NJ
;
LIU, YD
;
LEU, YJ
;
CHIANG, MY
The face selectivity in 5-substituted-adamantan-2-ones (1-Xs) can be dramatically reversed by means of inclusion into beta-cyclodextrin (beta-CD) and its heptakis(6-O-hydroxypropyl), heptakis(6-O-acetyl), heptakis(2,3,6-tri-O-methyl) and heptakis(2,3,6-tri-O-acetyl) derivatives. The 5-substituents varied from fluoro, chloro, bromo, phenyl to trimethylsilyl, and face selectivities of the oxetane formation have been found to vary with the sizes of 5-substituents and cavities of beta-CDs. A 98:2 face selectivity was achieved when 1-SiMe(3) was used as a probe. The effect observed is interpreted by assuming that the carbonyl pi-face syn to the bulky 5-substituent is partially locked by the torus of the host due to complexation of 1-X and CD. Information obtained from H-1 NMR titration and X-ray powder diffraction study on the inclusion complex is consistent with the above explanation. X-ray single-crystal structure was used to determine the oxetane structure of anti-2-SiMe(3).
SYNTHESIS AND CHARACTERIZATION OF CHIRAL SMECTIC SIDE-CHAIN LIQUID-CRYSTALLINE POLYSILOXANES CONTAINING 2,5-DISUBSTITUTED-1,3-DIOXANE BASED MESOGENIC SIDE-GROUPS
(1993)
JUANG, TM
;
LEU, YJ
;
HSU, CS
;
應用化學系
;
Department of Applied Chemistry
The synthesis of three liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxycarbonyl]phenyl 4-(trans-5-alkanyl-1,3-dioxan-2-yl]benzoates side groups is presented. The phase behavior of both monomeric and polymeric liquid crystals was characterized by optical polarizing microscopy, differential scanning calorimetry and X-ray diffraction measurements. The monomer which contains eleven methylene units in the spacers is the only one to exhibit the enantiotropic smectic A and chiral smectic C phases. The polymer containing six methylene units in the spacers presents an enantiotropic smectic A phase while the polymer containing eleven methylene units in the spacers shows an enantiotropic smectic A and a monotropic smectic B phase.