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相关概念视频

Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse.
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

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...
2D NMR: Overview of Homonuclear Correlation Techniques01:16

2D NMR: Overview of Homonuclear Correlation Techniques

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

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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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
14:55

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy

Published on: September 17, 2017

来自单个NMR实验的分子结构.

Eriks Kupce1, Ray Freeman

  • 1Varian Limited, 6 Mead Road, Yarnton, Oxford, OX5 1QU, UK.

Journal of the American Chemical Society
|July 23, 2008
PubMed
概括
此摘要是机器生成的。

这项研究提出了一种新的NMR方法,以高效地确定小分子结构. 它将多个NMR实验结合到一个通过中,简化结构分析.

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Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
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科学领域:

  • 有机化学 有机化学
  • 分析化学 分析化学
  • 频谱学是一种光谱学.

背景情况:

  • 核磁共振 (NMR) 光谱对于分子结构的确定至关重要.
  • 传统的NMR方法通常需要进行多次实验,增加时间和资源需求.
  • 高效和全面的结构阐明仍然是小分子分析的关键挑战.

研究的目的:

  • 开发一种精简的NMR程序,用于快速确定小分子结构.
  • 将基本结构信息获取集成到一个单一的NMR实验中.
  • 提高基于NMR的结构分析的效率.

主要方法:

  • 一个单一的NMR实验,结合了多个标准的NMR序列.
  • 并行获取二维碳-13碳-13相关性 (不充分),碳-13-1相关性 (单键和多键),以及传统的碳-13频谱.
  • 使用单独的接收通道来采集碳-13和-1信号.
  • 采用一种高灵敏度的冷冷却探头,优化用于碳-13检测.
  • 序列的扩展包括自然丰富的-15光谱,使用三个并行接收器.

主要成果:

  • 在单个NMR通过中成功获取基本结构信息.
  • 为各种NMR实验进行并行数据收集的演示.
  • 高灵敏度检测自然丰富的碳-13碳-13相关性.
  • 将-15光谱数据纳入综合实验的可行性.

结论:

  • 开发的 开发的 开发的
  • 所有在一个-all-in-one.
  • 核磁共振程序显著提高了小分子结构确定效率.
  • 这种综合方法从单个实验中提供了全面的结构数据,节省了时间和资源.
  • 该方法可适应包括其他核,如-15,进一步扩大其适用性.