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相关概念视频

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

912
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...
912
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

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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...
1.0K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

957
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,...
957
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.4K
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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Valence Bond Theory02:42

Valence Bond Theory

8.5K
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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¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

1.1K
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
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来自自旋转交叉车综合体的声学排放.

Sarah M Kamel1,2, Lajos Daróczi1, László Z Tóth1

  • 1Department of Solid State Physics, Doctoral School of Physics, University of Debrecen P.O. Box 2 H-4010 Debrecen Hungary dbeke@science.unideb.hu.

Journal of materials chemistry. C
|April 29, 2024
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概括

在铁化合物中旋转转变过程中检测到声辐射信号,与微观结构变化有关. 尽管旋转转换是可逆的,但随着周期的推移,声学活动下降,这表明样本的演变是不可逆的.

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科学领域:

  • 材料科学 材料科学 材料科学
  • 固态物理 固态物理
  • 化学 化学 化学

背景情况:

  • 旋转交叉 (SCO) 材料表现出高旋转和低旋转状态之间的过渡.
  • 热诱导的SCO可能涉及显著的体积和微观结构变化.
  • 声波发射 (AE) 是一种对动态过程和材料变化敏感的技术.

研究的目的:

  • 为了研究铁中热诱导的旋转转换过程中的声学辐射 (II) SCO复合体.
  • 为了将AE信号与热量计数据相关联,以了解辐射的物理来源.
  • 探索SCO材料在热循环过程中的微结构演变.

主要方法:

  • 在加热和冷却周期期间检测声学发射信号.
  • 同时测量热量计数据 (DSC) 以监测旋转转变.
  • 对AE信号振幅和能量概率分布函数的分析.
  • 研究AE事件 (雪崩) 的时间形状.

主要成果:

  • 在[Fe(HB(tz) 3) 2和[Fe(Htrz) trz) 2的旋转过渡过程中检测到声波发射并与热量计信号相关联.
  • AE信号归因于旋转过渡期间体积和微观结构变化产生的弹性波.
  • 随着连续的热周期,AE活动下降,尽管旋转转换是可逆的,这表明不可逆的微观结构进化.
  • AE振幅和能量分布遵循两样样样本具有相似指数的功率定律行为,表明普遍性.

结论:

  • 声波辐射是微观结构变化的敏感探测器,伴随着SCO材料的旋转转变.
  • 这些SCO材料在热循环中发生不可逆转的微结构演变,即使自旋转变化本身是可逆的.
  • 观察到的力量定律行为和缩放的雪崩形状表明旋转过渡过程中的普遍关键动态.