在1,2-dihydro-1,2-azaborines中发现电子移位的水晶清晰的结构证据
Eric R Abbey1, Lev N Zakharov, Shih-Yuan Liu
1Department of Chemistry, University of Oregon, Eugene, Oregon 97403, USA.
Journal of the American Chemical Society
|May 16, 2008
概括
研究人员已经从结构上描述了芳香前1,2-二-1,2-azaborines. 这些发现揭示了非局部化的键,证实了这些新的六个成员BN异环中的芳香性.
科学领域:
- 有机化学 有机化学
- 异环化学 异环化学
- 材料科学 材料科学 材料科学
背景情况:
- 芳香性是化学的一个基本概念,对于理解分子稳定性和反应性至关重要.
- 由于其独特的电子性质和潜在的应用,六分子- (BN) 异环具有兴趣.
- 在BN异环中,特别是那些具有部分和环的异环中,获得芳香度的途径仍然是积极研究的领域.
研究的目的:
- 合成和结构性地描述了第一批"预芳香"1,2-二-1,2-阿扎波林异环环的例子.
- 为了使这些系统中的非局部化结合与非芳香类型的局部化结合之间的直接比较.
- 阐明六个成员的BN异环在接近芳香度时发生的结构转换.
主要方法:
- 使用单晶X射线衍射分析来确定精确的分子结构.
- 使用光谱技术来确认电子特性和粘合特性.
- 使用计算方法来补充实验数据并分析电子移位.
主要成果:
- 首次实现了"芳香前"1,2-二-1,2-阿扎波林的结构性表征.
- 结晶学数据提供了前所未有的洞察力,了解六个成员的BN-异环中向芳香度的结构演变.
- 这项研究确定了1,2-二-1,2-阿扎波林表现出与芳香性相一致的非局部结构.
结论:
- 1,2-二-1,2-阿扎博林代表了一类重要的"预芳香"化合物.
- 结构数据明确表明,这些异环环中存在芳香性质.
- 这些发现有助于进一步了解含有BN的环系统中的芳香度,并为新材料设计打开了道路.
相关概念视频
01:18Structure of Benzene: Molecular Orbital Model
According to the molecular orbital (MO) model, benzene has a planar structure with a regular hexagon of six sp2 hybridized carbons. As shown in Figure 1, each carbon is bonded to three other atoms with C–C–C and H–C–C bond angles of 120°. The C–H bond length is 109 pm, and the C–C bond length is 139 pm which is midway between the single bond length of sp3 hybridized carbons (154 pm) and sp2 hybridized carbons (133 pm).
01:18Aromatic Hydrocarbon Cations: Structural Overview
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 with both...
Removing one hydrogen from the intervening CH2 group with both...
04:01VSEPR Theory and the Effect of Lone Pairs
Effect of Lone Pairs of Electrons on Molecule Geometry
01:18Aromatic Hydrocarbon Anions: Structural Overview
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 overlap of p...
Due to the absence of continuous overlap of p...
01:07Structure of Benzene: Kekulé Model
In 1865, August Kekule suggested the structure of benzene according to the structural theory of organic chemistry based on the three assertions—formula of benzene is C6H6, all the hydrogens of benzene are equivalent, and each carbon must have four bonds due to its tetravalency.
He proposed that benzene has a cyclic structure of six carbon atoms attached to one hydrogen atom each, with three alternating pi bonds.
He proposed that benzene has a cyclic structure of six carbon atoms attached to one hydrogen atom each, with three alternating pi bonds.
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.