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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 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...
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Aryldiazonium Salts to Azo Dyes: Diazo Coupling01:11

Aryldiazonium Salts to Azo Dyes: Diazo Coupling

The reaction of weakly electrophilic aryldiazonium (also called arenediazonium) salts with highly activated aromatic compounds leads to the formation of products with an —N=N— link, called an azo linkage. This reaction, presented in Figure 1, is known as diazo coupling and occurs without the loss of the nitrogen atoms of the aryldiazonium salt. Highly activated aromatic compounds such as phenols or arylamines favor the diazo coupling reaction. The coupling generally occurs at the para position.
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

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.

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相关实验视频

Updated: Jul 7, 2026

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes
12:07

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Published on: April 1, 2013

对光响应DNA与阿佐本结合的NMR研究. 在变形体中分配两个二聚体的绝对配置,并确定它们的双重体的结构.

Xingguo Liang1, Hiroyuki Asanuma, Hiromu Kashida

  • 1Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.

Journal of the American Chemical Society
|December 25, 2003
PubMed
概括

光响应DNA中的奇拉性影响结构和稳定性. 由于减小了螺旋应力,R型亚博烯-奥利戈氧核酸复合体显示出比S型更高的化温度.

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科学领域:

  • 分子生物学分子生物学
  • 有机化学 有机化学
  • 生物物理学的生物物理.

背景情况:

  • 光响应性小氧化核酸化合物包含阿佐为光控制的DNA相互作用.
  • 链接分子的性可以影响改性核酸的特性.

研究的目的:

  • 合成和分离一个光响应性寡氧化核酸的二聚体.
  • 阐明链接体性对DNA双重构成的结构和热力学影响.

主要方法:

  • 逆相高性能液态染色学 (RP-HPLC) 用于二聚体分离.
  • 二维核磁共振 (2D NMR) 谱学用于结构确定.
  • 化温度 (Tm) 分析以评估双重稳定性.

主要成果:

  • 通过成功地分离了与亚博结合的寡氧化核酸的两个二聚体 (R-和S-形式).
  • 2D核磁共振证实了这两种异构体中的基对之间的跨-亚基互.
  • 两种修改后的双重体都比原生双重体具有更高的化温度,这表明它们被酸稳定.
  • R型复合体表现出比S型复合体更高的化温度.

结论:

  • 二醇连接器的中心碳的性决定了二聚体的绝对配置 (R或S).
  • 间隔的跨-亚烯通过堆叠相互作用稳定了DNA复合体.
  • R型二聚体形成了一个比S型更稳定的复合体,这是由于R型的螺旋应力减少.
  • 这些发现凸显了立体化学在设计功能核酸类似物时的重要性.