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相关概念视频

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

1.0K
Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the...
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Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

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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...
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Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

928
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,...
928
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

951
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
951
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.0K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.0K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.2K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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从线性振动合模型对溶液相旋转动力学进行近似的哈密尔顿数.

Toby R C Thompson1, Jakob K Staab1,2, Nicholas F Chilton1,3

  • 1Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.

Journal of chemical theory and computation
|January 17, 2025
PubMed
概括

线性振动合 (LVC) 模型有效地接近分子哈密尔顿数. 精确的旋转动力学模拟对于兰坦化物复合物需要每10 fs重新参数化LVC.

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科学领域:

  • 计算化学计算化学
  • 量子力学就是量子力学.
  • 频谱学是一种光谱学.

背景情况:

  • 线性振动合 (LVC) 模型对微小的几何变化近似分子哈密尔顿数.
  • 对于特定应用,LVC提供了一个计算效率高的替代方案,而不是多配置的初始计算.
  • 精确建模复杂分子中的自旋动力学对于理解它们的特性至关重要.

研究的目的:

  • 为了研究LVC模型的应用,用于预测化兰化物复合物的自旋哈密尔顿数.
  • 在室温分子动力学轨迹上评估LVC近似自旋哈密尔顿数的准确性.
  • 为了确定对定量精确的旋转动力学模拟所需的LVC重新参数化的频率.

主要方法:

  • 使用线性振动合 (LVC) 模型来近似旋转哈密尔顿数.
  • 预测的近似旋转哈密尔顿数沿着一个溶解兰坦化物复合物的室温分子动力学轨迹.
  • 进行了自旋动态的依赖时间的量子模拟,使用LVC预测和ab initio预测的哈密尔顿数进行比较.

主要成果:

  • 随着分子几何形状与参数化参考不同,LVC近似的准确性下降.
  • 当LVC参数化在轨道期间至少每10 femtosecond (fs) 执行一次时,就能实现定量精确的旋转动态.
  • 与ab initio计算的比较验证了关于LVC准确性和重新参数化要求的发现.

结论:

  • 可以有效地使用LVC模型来近似旋转哈密尔顿数,用于兰坦化物复合物的分子动力学模拟.
  • 定期重新参数化LVC模型 (每10 fs) 对于保持旋转动力学模拟的定量准确性至关重要.
  • 这种方法提供了一个计算上可行的方法来研究复杂分子系统中的自旋动力学.