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相关概念视频

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

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

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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
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

978
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,...
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Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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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...
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Valence Bond Theory

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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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Support Reactions in Three Dimensions01:27

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Support reactions in three dimensions help maintain the stability and equilibrium of various structures and systems. These reactions prevent the system from translating and rotating, ensuring the design can withstand external forces and perform its intended function efficiently and safely. Some of the supports providing support reactions in three dimensions are discussed below:
Ball and Socket Joint is one of the supports allowing free rotation about any axis. This freedom of rotation is...
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旋转适应的外部承包的多引用配置交互方法基于选择的参考配置的交互方法.

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概括
此摘要是机器生成的。

对于大型系统,选择的配置交互 (sCI) 方法得到了改进. 使用配置状态函数和先进算法的新方法提高了量子化学计算中的动态相关性效率和准确性.

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科学领域:

  • 量子化学 是一个量子化学.
  • 计算化学计算化学

背景情况:

  • 选择配置交互 (sCI) 是对完整配置交互的近似,对大型活动空间有价值.
  • 动态相关性对于超出大型活动空间的定量结果至关重要.
  • 使用sCI引用的外部承包的多引用配置交互 (EC-MRCI) 是有希望的,但也有缺点.

研究的目的:

  • 为了解决之前的sCI-EC-MRCI方法中的旋转污染和低效率.
  • 为大型量子系统开发一种更有效,更准确的计算方法.

主要方法:

  • 使用了配置状态函数 (CSF) 基础,而不是斯莱特决定因素.
  • 介绍了一种混合算法,它结合了用于配置空间管理的树结构和用于矩阵元素计算的图形单元组方法 (GUGA).
  • 开发了一种旋转适应的方法版本.

主要成果:

  • 以旋转调整的CSF为基础的方法实现了6.0的加快速度,相比纳烯的斯莱特决定性版本.
  • 改进的sCI-EC-MRCI方法为双核铜 (II) 化合物和Ln (III) /An (III) 复合物提供了定量准确的结果.
  • 证明了将超越sCI的动态相关性纳入大型活动空间和基础集的能力.

结论:

  • 新的基于CSF的sCI-EC-MRCI方法显著提高了效率,并减少了旋转污染.
  • 这种方法可以准确地处理具有大型活性空间和基础集的复杂系统中的动态相关性.
  • 开发的计算策略对于在量子化学中挑战化学系统是有效的.