イメージングは,アルコキシ種のTiO上の回転を妨げました
Zhenrong Zhang1, Roger Rousseau, Jinlong Gong
1Fundamental and Computation Sciences Directorate and Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
Journal of the American Chemical Society
|November 26, 2009
まとめ
この研究は,スキャニングトンネル顕微鏡と計算方法を使用して,二酸化チタンの表面上のオクトキシ分子の回転ダイナミクスを明らかにします. アルキル鎖の回転は,表面相互作用と近くのヒドロキシル群によって妨げられます.
科学分野:
- 表面科学とは,地表科学である.
- 物理化学 物理化学
- マテリアルサイエンス 材料科学
背景:
- オキシード表面の分子行動を理解することは,触媒と電子工学にとって非常に重要です.
- 表面に吸収された有機種は,基板の相互作用によって影響される複雑なダイナミクスを示します.
研究 の 目的:
- ルチルTiOのオクトキシ種の回転ダイナミクスとコンフォーマーション障害をルチルTiO ((2) ((110)) 上で調査する.
- これらのダイナミクスを支配するヴァン・デル・ワールズ力とヒドロキシル群の役割を明らかにする.
主な方法:
- 変温スキャニングトンネル顕微鏡 (STM) を使用して,分子構成を視覚化しました.
- 分散補正密度関数理論 (DFT-D) の計算は,潜在エネルギー表面と回転障壁をモデル化するために行われました.
主要な成果:
- STMは,オクトキシ種の時間平均のスナップショットを明らかにし,複数の構成間で回転しています.
- DFT-Dの計算では,C...TiとC...O(b) の相互作用により,重要な回転障壁 (50-70 kJ mol(-1)) が特定されました.
- ゲミナートヒドロキシル群は,コンフォーメーション集団を混乱させ,C...ヒドロキシル反発を通して回転の障壁を増やすことが判明しました.
結論:
- TiO (((2) ((110) 上のオクトキシの回転ダイナミクスは,基板相互作用と隣接するヒドロキシル群の存在によって著しく影響を受けます.
- この研究は,酸化物表面上の有機吸着剤の行動に関する基本的な洞察を提供します.
さらに関連する動画
関連する概念動画
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
01:22Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.