当基环和环基环相遇时:光谱变化和构成问题
Luigi Villani1, Nishit R Mohire1, Evan G Robertson1
1Department of Biochemistry and Chemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia.
The journal of physical chemistry. A
|August 31, 2023
概括
研究人员使用先进的光谱学和量子计算研究了环烯 (CPB) 和环烯 (BrCPB). 他们确定了特定的分子结构,揭示了对形状偏好和光谱分配的见解.
科学领域:
- 物理化学 物理化学
- 分子光谱学 分子光谱学
- 计算化学计算化学
背景情况:
- 了解分子构造对于预测化学性质至关重要.
- 环烯及其衍生物由于环烯环而存在独特的结构挑战.
- 先进的光谱技术对于探测气相分子结构至关重要.
研究的目的:
- 研究气相中环烯 (CPB) 和1,3-烯烯 (BrCPB) 的电子和振动光谱.
- 使用实验和计算方法的组合来确定CPB和BrCPB的稳定对应子.
- 赋予特定的振动模式和电子过渡以阐明形状偏好.
主要方法:
- 共振增强多光子电离 (REMPI) 技术,包括1c-R2PI,UV-UV孔燃烧和IR-UV离子消耗光谱.
- 量子化学计算 (DFT) 用于建模电子和振动光谱.
- 分析CH拉伸振动和S1 ← S0过渡二极极矩 (TDM) 的对齐.
主要成果:
- 对于CPB和BrCPB,都确定了一个单一的稳定适应器,具有较低的相互转换障碍.
- 根据IR-UV光谱分析和DFT计算,CPB被分配给两截面的适配器.
- 使用TDM对齐分析将BrCPB分配给了"B1"两截式调整器,而"B2"调整器出乎意料地缺席.
结论:
- 该研究成功地在气相中分配了CPB和BrCPB在气相中占主导地位的对象.
- 过渡二极点瞬间的 conformational 灵敏性被证明对 BrCPB 赋值至关重要.
- 这些发现为在类似的受约束的阿里法系统中进行光谱分配提供了基础.
相关概念视频
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
877
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...
877
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
1.1K
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.
1.1K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
1.2K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
1.2K
NMR Spectroscopy of Benzene Derivatives
8.4K
Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling...
8.4K
IR and UV–Vis Spectroscopy of Aldehydes and Ketones
5.8K
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...
5.8K
Chair Conformation of Cyclohexane
14.8K
The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
14.8K


![Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F60786.jpg&w=3840&q=50)