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相关概念视频

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

936
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...
936
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

985
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,...
985
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.0K
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...
1.0K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

1.1K
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...
1.1K
The Pauli Exclusion Principle03:06

The Pauli Exclusion Principle

37.8K
The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that contains three pieces of information:
37.8K
Valence Bond Theory02:42

Valence Bond Theory

8.6K
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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相关实验视频

Updated: Jul 9, 2025

Spin Saturation Transfer Difference NMR SSTD NMR: A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes
11:44

Spin Saturation Transfer Difference NMR SSTD NMR: A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes

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一般化旋转 σ-SCF 方法

Ofelia B Oña1, Gustavo E Massaccesi2,3, Juan I Melo4,5

  • 1Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Universidad Nacional de La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas, Diag. 113 y 64 (S/N), Sucursal 4, CC 16, 1900 La Plata, Argentina.

The Journal of chemical physics
|December 4, 2023
PubMed
概括
此摘要是机器生成的。

我们介绍了一种新的σ-SCF方法,通过最小化哈密尔顿方差来找到非线性自旋状态,包括激发状态. 这种方法简化了在具有几何旋转挫折的系统中找到复杂的旋转结构.

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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
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Spin Saturation Transfer Difference NMR SSTD NMR: A New Tool to Obtain Kinetic Parameters of Chemical Exchange Processes
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Site Directed Spin Labeling and EPR Spectroscopic Studies of Pentameric Ligand-Gated Ion Channels
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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
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科学领域:

  • 量子化学是一种量子化学.
  • 计算物理学的计算物理.
  • 材料科学是一种材料科学.

背景情况:

  • σ-SCF方法通过最小化哈密尔顿方差来近似电子状态.
  • 准确地描述非对线性自旋状态,特别是激发状态,在量子化学中仍然是一个挑战.

研究的目的:

  • 概括 σ-SCF 方法用于近似非线性自旋基和激发状态.
  • 开发一种计算方法,以同等方式对待地面和激发的非线性自旋状态.
  • 为了研究表现出几何旋转挫折的系统.

主要方法:

  • 引入了一种通用的σ-SCF方法,最大限度地减少哈密尔顿变量.
  • 实施了两阶段的方法:模拟化用于广泛的探索和中场代用于融合.
  • 在模拟化过程中利用密度矩阵的随机复杂旋转.
  • 采用有效的Fockian从自相一致的现场阶段的差异中获得.

主要成果:

  • 成功地近似了非对线旋转地面和兴奋状态.
  • 证明了该方法在没有复杂的初始猜测操纵的情况下找到复杂的旋转结构的能力.
  • 将该方法应用于具有几何旋转挫折的Hn (n=3-7) 环和集群.
  • 在这些系统中确定了非线性旋转激发状态,与几何旋转丧有关.

结论:

  • 概括的σ-SCF方法有效地发现了近似的非线性自旋结构作为平均场激发状态.
  • 该方法为研究具有几何旋转挫折的系统提供了强大的工具.
  • 这种方法克服了能量最小化方法在准激发状态方面的局限性.