Browsing by Author "Chu, JH"

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Face selectivity in the reactions of 2,4-disubstituted adamantanes and their modification by inclusion in beta-cyclodextrin solutions
(2004-10-11)
Chu, JH
;
Li, WS
;
Chao, I
;
Chung, WS
;
應用化學系
Sodium borohydride reduction reactions on 4-X-adamantan-2-ones (where X=ethyleneketal 11, ethylenethioketal 12, and methylene 15) were studied, which gave Z-alcohols 16 and 17 (from en-face attack) as the predominant products for ketones 11 and 12, but gave 1: 1 mixture of Z- and E-18 alcohols for ketone 15. The en/zu face selectivity of 15 in sodium borohydride reduction was enhanced to 32/68 in beta-CD solution. Both 1,3-dipolar addition and dichlorocarbene addition reactions on 4-ethyleneketal-2-methyleneadamantane 13 underwent again predominant en-face attack to give products in an E/Z ratio of > 99:1 and 92:8, respectively. The exceptional high zu-face selectivity on the dichlorocarbene addition reaction of 15 may be explained by a temporal complexation between the carbene and the C-4-oxo group. In the epoxidation reaction of 13 and 15 the zu-face attack products were favored despite their steric congestions suggesting that hydrogen bonding interaction between the peroxide reagent and the C-4-oxo or 4-ethyleneketal is involved. (C) 2004 Elsevier Ltd. All rights reserved.
Face selectivity in the reactions of 2,4-disubstituted adamantanes.
(2000-08-20)
Chung, WS
;
Chu, JH
;
應用化學系
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Department of Applied Chemistry
Slow light in photonic crystals
(2005-03-01)
Chu, JH
;
Voskoboynikov, O
;
Lee, CP
;
電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
In this work we demonstrate an interesting opportunity to decrease drastically the group velocity of light in two-dimensional photonic crystals constructed form materials with large dielectric constant without dispersion (epsilon(d) similar to 100). The group velocity of light in the crystals can be lowered up to 10(-5) - 10(-4) c (c is velocity of light in free space) in a wide range of the Brillouin zone. We propose a simple and general explanation why that should appear in photonic crystals with large dielectric constants. (c) 2005 Elsevier Ltd. All rights reserved.