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相关概念视频

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 Labile Protons: Deuterium (²H) Substitution00:48

¹H NMR of Labile Protons: Deuterium (²H) Substitution

This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is the use of deuterium. Amongst the three isotopes of hydrogen, deuterium (2H) has a nucleus composed of one proton and one neutron. When the D2O solvent is added to a pure dry ethanol solution, its labile proton is substituted with deuterium.
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)01:20

¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)

When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
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...
NMR Spectroscopy Of Amines01:19

NMR Spectroscopy Of Amines

In proton NMR spectroscopy, primary amines and secondary amines showcase their N–H protons as a broad signal in the chemical shift range between δ 0.5 and 5 ppm. The exact position in this range depends on several factors, including sample concentration, hydrogen bonding, and the type of solvent used. Since amine protons undergo fast proton exchange in solution, the protons are labile and therefore do not participate in any splitting with adjacent protons. Thus, the observed peak is broad and...
Other Nuclides: 31P, 19F, 15N NMR01:16

Other Nuclides: 31P, 19F, 15N NMR

Many organic, inorganic, and biological molecules contain spin-half nuclei such as nitrogen-15, fluorine-19, and phosphorus-31. As a result, NMR studies of these nuclei have found extensive applications in chemical and biological research.
While fluorine-19 and phosphorous-31 have high natural abundances (100%) and positive gyromagnetic ratios, nitrogen-15 has a low natural abundance and a negative gyromagnetic ratio. However, nitrogen-15 is still preferred over nitrogen-14 (which has a high...

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相关实验视频

Updated: Jul 11, 2026

Methods to Identify the NMR Resonances of the 13C-Dimethyl N-terminal Amine on Reductively Methylated Proteins
13:59

Methods to Identify the NMR Resonances of the 13C-Dimethyl N-terminal Amine on Reductively Methylated Proteins

Published on: December 12, 2013

乳标记和NMR研究N--N-基基基酸胺通过阴离子循环的dearomatization:由复杂诱导的近距离效应指导的正极和基化.

Ignacio Fernández1, Javier González, Fernando López-Ortiz

  • 1Area de Química Orgánica, Universidad de Almería, Carretera de Sacramento s/n, Almería, Spain.

Journal of the American Chemical Society
|September 30, 2004
PubMed
概括
此摘要是机器生成的。

这项研究揭示了使用标记和NMR的胺胺的阳离子循环 dearomatization 机制. 它确定了关键的阳离子物种和通路,显示HMPA催化了关键的转位.

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相关实验视频

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Methods to Identify the NMR Resonances of the 13C-Dimethyl N-terminal Amine on Reductively Methylated Proteins
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科学领域:

  • 有机金属化学 有机金属化学
  • 反应机制 解 反应机制
  • 酸盐化学 酸盐化学

背景情况:

  • 了解阳离子循环化和 dearomatizing 反应对于合成化学至关重要.
  • 基和协调溶剂在复杂反应路径中的作用需要详细的研究.
  • N-基-N-甲基基胺作为探索复杂的有机金属转换的模型基质.

研究的目的:

  • 阐明N-基-N-甲基二四胺胺的离离子循环化脱芳反应的详细机制.
  • 为了识别和描述反应途径中涉及的过渡性阴离子物种.
  • 调查协调辅溶剂,如甲基胺 (HMPA) 对反应机制的影响.

主要方法:

  • 乳标记研究,以追踪反应中间体和途径.
  • 自然丰富的多核磁共振 (NMR) 光谱,包括 (1) H, (2) H, (7) Li, (13) C,和 (31) P.
  • 二维 (2D) 核磁共振技术,特别是 (7) Li,(31) P[(1) H] 转移相关性和 (7) Li[(31) P] 核磁共振,用于结构性赋值.

主要成果:

  • 在没有HMPA的情况下识别了八种主要的阳离子物种,揭示了化反应路径.
  • 有证据表明,复合体诱导的近距离效应 (CIPE) 涉及二维预复合体和随后的基和正极脱离子离子的形成.
  • 证明可逆的分子内合添加和HMPA在促进转位和循环化的催化作用.

结论:

  • 该研究成功地揭开了复杂的反应机制,包括多种阴离子物种的形成和相互转换.
  • 这些发现强调了协调和溶剂作用在指导反应途径方面的重要性.
  • 先进的NMR技术对过渡性中间体的结构阐明和理解立体化学方面至关重要.