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関連する概念動画

Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

678
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.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
678
NMR Spectroscopy: Chemical Shift Overview01:15

NMR Spectroscopy: Chemical Shift Overview

1.6K
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.
For instance, the proton...
1.6K
Molecular and Ionic Solids02:54

Molecular and Ionic Solids

17.3K
Crystalline solids are divided into four types: molecular, ionic, metallic, and covalent network based on the type of constituent units and their interparticle interactions.
Molecular Solids
Molecular crystalline solids, such as ice, sucrose (table sugar), and iodine, are solids that are composed of neutral molecules as their constituent units. These molecules are held together by weak intermolecular forces such as London dispersion forces, dipole-dipole interactions, or hydrogen bonds, which...
17.3K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

1.2K
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...
1.2K
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

1.1K
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
1.1K
Inductive Effects on Chemical Shift: Overview01:27

Inductive Effects on Chemical Shift: Overview

1.2K
The protons in unsubstituted alkanes are strongly shielded with chemical shifts below 1.8 ppm. Methine, methylene, and methyl protons appear at approximately 1.7, 1.2 and 0.7 ppm, while the proton signal from methane appears at 0.23 ppm. An electronegative substituent, such as chlorine, withdraws the electron density from the protons, increasing their chemical shift. Progressive substitution of the hydrogens in methane by chlorine shifts the proton signals increasingly downfield, to 3.05 ppm in...
1.2K

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関連する実験動画

Updated: Jul 23, 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

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分子固体における化学的シフト依存相互作用マップ

Manuel Cordova1,2, Lyndon Emsley1,2

  • 1Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.

Journal of the American Chemical Society
|July 13, 2023
PubMed
まとめ
この要約は機械生成です。

この研究では,分子構造と実験的化学変化から派生した 3D 相互作用マップが紹介されています. これらのマップは,結晶構造予測 (CSP) を加速し,計算的に集中的な DFT 計算なしで候補構造を評価します.

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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
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Author Spotlight: Exploring Cellular Processes by Modeling Ligands in Cryo-EM Maps
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関連する実験動画

Last Updated: Jul 23, 2025

Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
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Author Spotlight: Exploring Cellular Processes by Modeling Ligands in Cryo-EM Maps
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科学分野:

  • 固体化学
  • クリスタルグラフィー
  • コンピュータ化学

背景:

  • NMR結晶学は分子固体構造を決定する鍵です.
  • 結晶構造予測 (CSP) プロトコルは計算が集中しており,ポリモルフ探索を妨げています.
  • 候補結晶構造の生成はCSPのボトルネックです.

研究 の 目的:

  • 結晶構造予測 (CSP) プロトコルを加速する方法を開発する.
  • 候補結晶構造の確率を効率的に評価する.
  • CSPに関連する計算コストを削減する.

主な方法:

  • 結晶構造と実験的化学変化のデータベースから3次元相互作用マップを構築する.
  • 分子構造と関連する実験的化学変化から直接地図を導きます.
  • これらの地図を使用して,CSPの構造的制約を特定します.

主要な成果:

  • CSPプロトコルを加速させるための構造的制約を特定する能力を示した.
  • DFT計算なしで候補結晶構造を評価する方法を紹介した.
  • 固体構造の決定のための新しいツールとして3Dインタラクションマップを開発しました.

結論:

  • 3Dインタラクションマップは,CSPを加速させるための計算効率の良いアプローチを提供します.
  • 開発された方法は,候補結晶構造を生成する際のボトルネックを軽減します.
  • この技術は,結晶構造候補を評価するための実行可能な代替手段を提供します.