来自H NMR和UV-Vis吸收数据的芳香化能量直接估计的同位素分子
Puthiyavalappil K Arathi1,2, Cherumuttathu H Suresh1,2
1Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram 695019, India.
The Journal of organic chemistry
|July 23, 2024
概括
这项研究用环开反应量化了各种环系中的芳香稳定能量 (Ea). 结果显示了Ea,NMR化学转移和UV-vis光谱之间的相关性,用于预测芳香度.
科学领域:
- 计算化学计算化学
- 有机化学 有机化学
- 频谱学是一种光谱学.
背景情况:
- 迪亚利-环-皮兰系统经历环开放反应,形成 cis-ortho quinonoid 结构.
- 芳香能量 (Ea) 是了解芳香和反芳香系统稳定的关键指标.
- 现有的Ea测定方法可能是复杂且资源密集的.
研究的目的:
- 为了研究二甲基-环-皮兰系统的环开放反应.
- 开发一种可靠的方法来评估各种环系统的芳香化能量 (Ea).
- 探索Ea与光谱特性 (NMR和UV-vis) 之间的关系.
主要方法:
- 利用密度函数理论 (DFT) 计算Ea用于各种芳香,反芳香和非芳香环形图案.
- 分析了同位素反应对来定义和量化Ea.
- 与实验1H NMR化学转移 (δavg) 和紫外线对吸收最大差异 (Δλavg) 相关联的计算Ea值.
主要成果:
- 对诸如 (23.4 kcal/mol) 和环丁 (-29.9 kcal/mol) 等系统的量化Ea,显示每个键的稳定/不稳定.
- 已确立的Ea和光谱参数之间的线性相关性: -1.0 ppm的NMR转移相当于24.2 kcal/mol.
- 证明UV-vis光谱数据可以使用适当的同位素对直接评估Ea.
结论:
- 环开放反应为评估芳香化能量提供了一个强大的框架.
- 光谱方法 (NMR和UV-vis) 为评估芳香稳定提供了实用和预测工具.
- 这种方法提高了对芳香化合物和反芳香化合物的能量和光谱特征的理解.
相关概念视频
NMR Spectroscopy of Aromatic Compounds
4.6K
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.
4.6K
UV–Vis Spectroscopy of Conjugated Systems
6.9K
Organic compounds with conjugated double bonds show strong absorption features in the UV–visible region of the electromagnetic spectrum attributed to π → π* electronic excitations. Generally, a UV–vis absorption spectrum is recorded as a plot of absorbance vs wavelength. The wavelength of maximum absorbance, which manifests as a peak in the absorption spectrum, is denoted as λmax.
One of the factors influencing λmax is the extent...
One of the factors influencing λmax is the extent...
6.9K
IR and UV–Vis Spectroscopy of Aldehydes and Ketones
5.4K
Infrared spectroscopy, also known as vibrational spectroscopy, is mainly used to determine the types of bonds and functional groups in molecules. In aldehydes and ketones, the carbonyl (C=O) bond shows an absorption around 1710 cm-1. The C=O bond vibration of an aldehyde occurs at lower frequencies than that of a ketone. In addition to the C=O absorption in an aldehyde, the aldehydic C–H bond also gives two peaks in the 2700–2800 cm-1 range. This absorption, coupled with the...
5.4K
UV–Vis Spectroscopy: Molecular Electronic Transitions
1.4K
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this...
1.4K
UV–Vis Spectroscopy: Woodward–Fieser Rules
24.1K
UV–Visible absorption spectra of conjugated dienes arise from the lowest energy π → π* transitions. The light-absorbing part of the molecule is called the chromophore, and the substituents directly attached to the chromophore are called auxochromes. A strong correlation exists between the absorption maxima, λmax, and the structure of a conjugated π system. The Woodward–Fieser rules predict the value of λmax for a given...
24.1K
IR Spectrum
970
When infrared (IR) radiation passes through a molecule, the bonds stretch or bend by absorbing the radiation. This absorption creates the molecule's absorption spectrum, which is the plot of its percentage transmittance versus wavenumber.
Transmittance is defined as the ratio of the radiant power passing through a sample to that from the radiation's source. Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0%...
Transmittance is defined as the ratio of the radiant power passing through a sample to that from the radiation's source. Multiplying the transmittance by 100 gives the percent transmittance (%T), which varies between 100% (no absorption) and 0%...
970


