相关实验视频
Updated: Aug 16, 2026

06:53
Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
Published on: July 27, 2018
在CH2D组中促进质子异时性
Benjamin D Allen1, Daniel J O'Leary
1Department of Chemistry, Pomona College, 645 North College Avenue, Claremont, CA 91711-6338, USA.
Journal of the American Chemical Society
|September 17, 2004
概括
一种新的C-D...N相互作用产生了显著的同位素效应,导致NMR光谱学中的化学转移差异很大. 这一发现有助于确定使用NMR的立体甲基组的配置和纯度.
科学领域:
- 有机化学 有机化学
- 核磁共振 (NMR) 光谱学 核磁共振 (NMR) 光谱学
- 计算化学的计算化学
背景情况:
- 在NMR光谱学中,同位素效应对于理解分子结构和动态至关重要.
- (D) 标签是一种用于探测分子相互作用和立体化学的常见技术.
- (N-CH2D) - - - - - - 异分离子离子为研究C-D...N相互作用提供了一个独特的系统.
研究的目的:
- 研究一种新的C-D...N相互作用及其对NMR化学转移的影响.
- 探索该系统的潜力,以确定立体甲基组的配置和反体纯度.
- 验证ab initio计算方法来预测NMR中的同位素效应.
主要方法:
- 实验性NMR光谱 (特别是NMR) 用于测量化学转移差异.
- 最初的计算协议被用来预测和分析观察到的同位素效应.
- 实验数据与对异分离子离子和相关的piperidine系统的理论预测进行比较.
主要成果:
- 由于C-D...N相互作用,在 (N-CH2D) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 的 (N-CH2D) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 的异位基质中,在22°C时观察到43ppb的显著化学转移差异.
- 实验结果与从一开始计算的理论预测 (44 ppb) 密切匹配.
- 计算方法准确地复制了相关的化皮佩里丁系统 (17ppb vs. 14ppb) 的实验数据.
结论:
- 这项研究表明,一种新的C-D...N相互作用可以诱导相当大的平衡同位素效应.
- 这些发现表明,异二烯衍生系统提供了一个有前途的方法,可以通过三NMR来赋予立体甲基组的配置和反体纯度.
- Ab initio计算被验证为预测和理解复杂有机分子中这些同位素效应的可靠工具.
相关概念视频
Prochirality
The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
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.
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
Diazonium Group Substitution: –OH and –H
Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.
π Electron Effects on Chemical Shift: Overview
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, resulting in...
¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons
Replacing each alpha-hydrogen in chloroethane by bromine (or a different functional group) yields a pair of enantiomers. Such protons are called prochiral or enantiotopic and are related by a mirror plane. Enantiotopic protons are chemically equivalent in an achiral environment. Because most proton NMR spectra are recorded using achiral solvents, enantiotopic hydrogens yield a single signal.
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...

