通过堆叠改变芳香性质:面对面的Ni (II) bis (pentafluorophenyl) 或corrole的二元体
Qian Wang1, Dage Sundholm1, Jürgen Gauss2
1Department of Chemistry, Faculty of Science, University of Helsinki, P.O. Box 55 (A.I. Virtanens plats 1), FIN-00014, Finland. Dage.Sundholm@helsinki.fi.
Physical chemistry chemical physics : PCCP
|May 8, 2024
概括
核磁共振 (NMR) 屏蔽常数是为含的诺克罗单体和二元体计算的. 研究显示单体是反芳香的,而二元体由于分子间相互作用而表现出芳香性.
科学领域:
- 计算化学计算化学
- 量子化学 是一个量子化学.
- 材料科学 材料科学 材料科学
背景情况:
- 核磁共振 (NMR) 光谱是一种强大的工具,用于表征分子结构和电子性质.
- 了解像诺科罗尔这样的宏环化合物的电子结构对于它们在各种领域的应用至关重要.
- 堆叠系统中的分子间相互作用可以显著改变电子性质,导致新的行为.
研究的目的:
- 计算和比较一个Ni(II) bis(pentafluorophenyl) norcorrole单体及其面对面堆叠的二次体的NMR屏蔽常数.
- 调查单体和二元体的电子特性,包括磁诱导电流密度.
- 阐明分子间相互作用在堆叠二次体的芳香性和电子结构中的作用.
主要方法:
- 使用了包括Hartree-Fock (HF),Møller-Plesset扰动理论 (MP2),完全活性空间自相一致场 (CASSCF) 和密度函数理论 (DFT) 在内的高级计算化学方法.
- 计算了1H,N和Ni核的NMR屏蔽常数.
- 计算了磁诱导电流密度,以评估芳香度和环流.
主要成果:
- 计算的1H NMR屏蔽常数与实验数据有很好的一致性.
- 在DFT/HF/MP2和CASSCF方法之间观察到N和Ni屏蔽常数的显著差异,归因于Ni原子的近退化效应.
- 诺科罗尔单体表现出强烈的全球偏热环电流的抗芳香性.
- 面对面堆叠的二极管显示了具有强烈二极管环电流的芳香性,这归因于短的分子间距离 (<3 Å).
- 在二分体中的分子间相互作用导致边界轨道的改变和宏循环之间的正式双键.
结论:
- 这项研究提供了对Ni (II) 或corrole系统的电子结构和芳香度的宝贵见解.
- 计算方法,特别是MP2,可以准确预测环电流强度.
- 面对面堆叠的norcorrole宏循环可以诱导芳香性,并创建新的结合相互作用,表明新的材料设计的潜力.
相关概念视频
01:18Aromatic Hydrocarbon Cations: Structural Overview
2.8K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
Removing one hydrogen from the intervening CH2 group...
2.8K
01:18Aromatic Hydrocarbon Anions: Structural Overview
2.8K
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous...
Due to the absence of continuous...
2.8K
01:13Five-Membered Heterocyclic Aromatic Compounds: Overview
3.9K
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom,...
3.9K
01:14π 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
01:18Frost Circles for Different Conjugated Systems
2.7K
The inscribed polygon method is consistent with Hückel’s 4n + 2 rule and helps to learn whether the given cyclic compound is aromatic or not. The compound is stable and aromatic if every bonding molecular orbital (MO) is completely filled with a pair of electrons. However, if the non-bonding or antibonding orbitals are filled with electrons, the compound is unstable and not aromatic. Consider the Frost circle diagrams for cycloalkenes containing 4 to 8 carbons.
2.7K
01:20Criteria for Aromaticity and the Hückel 4n + 2 Rule
10.5K
Like benzene, cyclobutadiene and cyclooctatetraene are cyclic compounds with alternate single and double bonds. However, their chemical behavior differs from benzene, as they are unstable and not aromatic. So, what are the structural characteristics of unsaturated compounds categorized as aromatic?
For the first time, Eric Hückel, a German chemical physicist, derived a set of structural features for a compound to be classified as aromatic. This is now known as...
For the first time, Eric Hückel, a German chemical physicist, derived a set of structural features for a compound to be classified as aromatic. This is now known as...
10.5K