水溶液中のニトロベンゼンの超高速光化学ダイナミクスの解明
Nicholas A Lau1, Deborin Ghosh2, Susannah Bourne-Worster1
1Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K.
Journal of the American Chemical Society
|April 4, 2024
まとめ
ニトロベンゼンのようなニトロアロマティック化合物は,茶色の炭素の主要成分です. 水中では,彼らの光化学反応は水素結合とエネルギー伝達によって遅くなり,光産物の形成を防ぐ.
科学分野:
- 大気化学
- 写真化学
- スペクトロスコーピー
背景:
- ニトロアロマティック化合物を含む茶色の炭素のエアロゾールは,太陽放射線を吸収することで地球の気候に大きく影響を与えます.
- 雲や霧の液体の水性光化学は 茶色の炭素の重要な二次源です
- ニトロベンゼンは大気中のより大きなニトロアロマティック分子の光化学的振る舞いを理解するためのモデル化合物として機能する.
研究 の 目的:
- 紫外線に近い光刺激による水溶液中のニトロベンゼンの超高速光化学的動態を調査する.
- 周囲の溶媒環境 (水,メタノール,アセトニトリル,サイクロヘキサン) がニトロベンゼンの光化学プロセスに果たす役割を明らかにする.
- 水中の光化学とガス相の振る舞いを比較する.
主な方法:
- フェムトセカンド 暫定吸収スペクトロシー
- 時間解像度の赤外線スペクトル
- 量子化学の計算
- 比較溶剤試験 (水,メタノール,アセトニトリル,サイクロヘキサン)
主要な成果:
- 水性環境への振動エネルギー転送は,ニトロベンゼンの内部刺激を効果的に消し去ります.
- ガス相とは異なり,水溶液で500nsまでの時間スケールで光産物は見られなかった.
- ニトロベンゼンと水分子の間の水素結合は,S1/S0の内部変換プロセスを遅らせることが判明した.
結論:
- 水中の環境は,ガス相と比較して,ニトロベンゼンの光化学的経路を大幅に変化させる.
- 水素結合による振動エネルギー移転による消火と,水中の光産物形成を阻害する.
- これらの発見は,ナイトロアロマティック化合物の大気の運命と気候への影響を正確にモデル化するために重要です.
関連する概念動画
Electrophilic Aromatic Substitution: Nitration of Benzene
5.9K
The nitration of benzene is an example of an electrophilic aromatic substitution reaction. It involves the formation of a very powerful electrophile, the nitronium ion, which is linear in shape. The reaction occurs through the interaction of two strong acids, sulfuric and nitric acid.
5.9K
meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H
5.6K
All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...
5.6K
Rate-Determining Steps
32.4K
Relating Reaction Mechanisms
In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate.
The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...
In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate.
The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...
32.4K
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Mechanism
3.8K
Nitrous acid is a relatively weak and unstable acid prepared in situ by the reaction of sodium nitrite and cold, dilute hydrochloric acid. In an acidic solution, the nitrous acid undergoes protonation when it loses water to form a nitrosonium ion—an electrophile. Nitrous acid reacts with primary amines to give diazonium salts. The reaction is called diazotization of primary amines.
3.8K
Nucleophilic Aromatic Substitution: Elimination–Addition
4.0K
Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is...
4.0K
NMR Spectroscopy of Benzene Derivatives
8.2K
Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling...
8.2K


