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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.

Chemical Shift: Internal References and Solvent Effects

Chemical Shift: Internal References and Solvent Effects

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...

NMR and Mass Spectroscopy of Carboxylic Acids

NMR and Mass Spectroscopy of Carboxylic Acids

In ¹H NMR spectroscopy, acidic protons (–COOH) of carboxylic acids are highly deshielded and absorb far downfield, at around 9–12 ppm. The chemical shift value depends on the concentration and solvent used.
While α protons of carboxylic acids absorb at 2–2.5 ppm, β protons absorb further upfield.
Carboxylic acids are easily identified by dissolving them in deuterium oxide, which results in a rapid exchange of the acidic protons with deuterium. This leads to the...

NMR Spectroscopy of Aromatic Compounds

NMR Spectroscopy of Aromatic Compounds

Aromatic compounds can be identified or analyzed using proton NMR and carbon‐13 NMR. Typically, aromatic hydrogens or hydrogens directly bonded to the aromatic rings are strongly deshielded by the aromatic ring current. Therefore, they absorb in the range of 6.5–8.0 ppm in proton NMR spectra. For instance, aromatic hydrogens directly bonded to the benzene ring absorb at 7.3 ppm. However, aromatic hydrogens of larger rings absorb farther upfield or downfield than the ideal range.

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Updated: Jun 10, 2025

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

Published on: January 25, 2020

用不同溶剂的NMR数据验证宏循环化合物的小分子力场.

Franz Waibl¹, Fabio Casagrande², Fabian Dey²

¹Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland.

Journal of chemical information and modeling

|October 15, 2024

概括

此摘要是机器生成的。

现代计算方法,包括与溶液炼 (REST2) 模拟的复制品交换,可以准确预测宏循环化合物组合. 像OpenFF 2.0和XFF这样的新型力量场对药物设计具有前景,尽管某些情况下仍需要进一步开发.

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Author Spotlight: Advancing Cell Membrane Biophysics - Exploring Interactions and Challenges Through Experimental and Computational Approaches

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Published on: September 1, 2023

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Published on: December 16, 2013

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Last Updated: Jun 10, 2025

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

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Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Published on: December 16, 2013

科学领域:

计算化学是一种计算化学.
药物发现药物发现
分子建模分子建模

背景情况:

由于其独特的结合性质,宏循环为具有挑战性的目标提供治疗潜力.
准确预测宏环形态构成组合对于合理的药物设计至关重要.
分子动力学 (MD) 模拟很强大,但很大程度上取决于所使用的力场的准确性.

研究的目的:

为了对四个不同的力场进行基准测试,以确定它们预测宏循环形态构成组合的能力.
为了评估复制品交换的性能与溶液炼 (REST2) 对宏观循环的模拟.
将计算预测与核Overhauser效应 (NOE) 实验中的实验数据进行比较.

主要方法:

在11个宏环化合物上进行了REST2模拟.
与实验NOE距离限制器相比,模拟的形状组合.
评估的力场包括OpenFF 2.0,XFF,GAFF2和OPLS/AA.

主要成果:

现代力场OpenFF 2.0和XFF在预测宏循环组合方面表现良好.
这些现代力场的性能优于GAFF2和OPLS/AA等较旧的力场.
确定了所有测试的力场未能准确地重现实验数据的特定情况.

结论:

与现代力场相结合的 REST2 模拟经常可以产生准确的宏循环化合物组合.
选择合适的力场对于在宏循环药物设计中可靠的计算预测至关重要.
需要在力场方面取得进一步的进步,以解决预测某些宏观环形形态行为的局限性.