相关实验视频

Updated: Jun 28, 2025

Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
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Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks

Published on: June 9, 2023

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用量子化学方法深入研究用于准磁过渡金属系统中化学转移的准确计算的理论和计算考虑因素

Md Ashraful Islam1, Andrew J Pell1

  • 1Centre de RMN à Très Hauts Champs de Lyon, UMR-5082, CNRS/UCB Lyon 1/ENS de Lyon, 69100 Villeurbanne, France. ashraful.islam@ens-lyon.fr.

Physical chemistry chemical physics : PCCP
|April 15, 2024
PubMed
概括

这项研究引入了一种新的量子化学方法,用于计算过渡金属系统中的磁性化学转移. 该方法准确地解释了各种贡献,改善了核磁共振 (NMR) 光谱学的预测.

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In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
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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.
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The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
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