パラ磁性複合イオンによって触媒化されたパラ水素とオーソ水素の相互変換の動力学
Mitsuru Matsumoto1, James H Espenson
1Department of Chemistry, Iowa State University of Science and Technology, Ames, Iowa 50011, USA.
Journal of the American Chemical Society
|August 11, 2005
まとめ
パラ水素とオーソ水素 (p-/o-H2) の核スピンイソメリゼーションは,パラ磁性金属複合体によって触媒化されます. 速度の定数は磁気モーメントと相関し,ウィーネン運動を支えている.
科学分野:
- 物理化学 物理化学
- 化学動力学 化学動力学
- 核磁共振スペクトロスコーピー 核磁共振スペクトロスコーピー
背景:
- パラ/オルト水素 (p-/o-H2) 核スピンイソメリゼーションは,基本的な化学プロセスです.
- パラマグネティック複合イオンは,このイソメリゼーション反応の触媒として知られています.
- 反応速度を制御するために,触媒の性質を理解することは極めて重要です.
研究 の 目的:
- p-/o-H2核スピンイソメリゼーションの速度定数を測定するために.
- 触媒の特性 (磁気モメント,サイズ) と反応速度との関係を調査する.
- この触媒過程に対するウィーグナー理論の適用性を評価する.
主な方法:
- プロトン核磁気共鳴 (1H NMR) スペクトルスコピーは,速度常数測定に使用されました.
- 実験は,常温 (298.2 K) のデュテラート溶媒で実施した.
- 運動データを分析して,二次速度定数と有効衝突半径を決定した.
主要な成果:
- 速度定数は,触媒濃度に比例する.
- 2次方位定数は,3次元移行金属およびランタニド複合体の磁気モメントの正方形と正比を示しています.
- 3D移行金属複合体のレート定数には,リガンドの大きさが影響しますが,理論で予測されるよりも少ないです.
結論:
- 速度定数と磁気モメントの相関は,ウィーグナー理論と一致しています.
- 触媒のサイズは,予期していたよりも反応速度に大きな影響を与えない.
- 効果的な衝突半径は,ソルバット金属複合体の各シリーズ内で比較的一定である.
関連する概念動画
Atomic Nuclei: Magnetic Resonance
The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
Atomic Nuclei: Nuclear Relaxation Processes
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis. This...
Spin–Spin Coupling Constant: Overview
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Spin–Spin Coupling: One-Bond Coupling
Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
Transition State Theory
Transition-state theory, also known as activated-complex theory, provides a molecular-level explanation of reaction rates in both gas-phase and solution-phase reactions. It extends earlier kinetic models by considering the formation of a short-lived, high-energy configuration during a reaction.The progress of a chemical reaction can be represented using a reaction profile, which plots potential energy against the reaction coordinate. As two reactant molecules approach one another, their...
Reversible or Opposing Reactions
Reversible or opposing reactions play a crucial role in understanding the dynamic nature of chemical processes. While kinetics focuses on how reactions proceed, thermodynamics emphasizes that most reactions do not reach completion. Instead, a reverse reaction starts occurring over time, and when its rate equals that of the forward reaction, a dynamic equilibrium is established.For example, consider a simple chemical process where A forms B reversibly. The rate constants for the forward and...


