Browsing by Author "Yabushita, Atushi"

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Direct observation of denitrogenation process of 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) derivatives, using a visible 5-fs pulse laser
(2012-02-27)
Abe, Manabu
;
Iwakura, Izumi
;
Yabushita, Atushi
;
Yagi, Shingo
;
Liu, Jun
The mechanism of denitrogenation for 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) derivatives was investigated using a visible 5-fs pulse laser. The time-dependent wavenumber changes observed in this study revealed that the concerted denitrogenation occurs in the parent DBH. However, a stepwise denitrogenation mechanism was found for the 7,7-diethoxy-substituted DBH derivative. (C) 2012 Elsevier B. V. All rights reserved.
Direct Observation of the Molecular Structural Changes during the Claisen Rearrangement Including the Transition State
(2010-04-05)
Iwakura, Izumi
;
Yabushita, Atushi
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
The detailed processes in the Claisen rearrangement were observed. The process was vibrationally excited in the electronic ground state by a stimulated Raman process using a 5-fs pulse. The Claisen rearrangement was found to follow a three-step pathway. At first, the C(4)-O bond is weakened to generate a bis-allyl-like intermediate. Next, the formation of a weak C(1)-C(6) bond results in the generation of an aromatic-like intermediate. Finally, C(4)-O breaking and C(1)-C(6) formation occur simultaneously to generate the product.
Why is Indigo Photostable over Extremely Long Periods?
(2009-11-05)
Iwakura, Izumi
;
Yabushita, Atushi
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
This experimental work clarifies the mechanism for the Ultra-photostability of indigo carmine by direct observation of a transition state using a sub 5-fs laser pulse. The molecular structural changes during the photoexcited proton-transfer process were traced as the time-dependent instantaneous frequency of molecular vibrations. The mono-alcohol intermediate generated by proton transfer via stepwise path was found to be unstable, and it immediately reverted to indigo carmine. This regression to the reactant is the reason for the ultraphotostability of indigo over extremely long periods.