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Updated: Jan 18, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

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[6]环-甲:一种具有全球芳香性和开放的二基性特征的类

Zhengtao Li1, Tullimilli Y Gopalakrishna1, Yi Han1

  • 1Department of Chemistry , National University of Singapore , 3 Science Drive 3 , 117543 , Singapore.

Journal of the American Chemical Society
|October 1, 2019
PubMed
概括

我们合成了一种 [6]cyclo-para-phenylmethine ([6]CPPM) 宏循环,表现出类似的特性和二基性质. 这种"超"在中性和二状态下表现出全球芳香性和独特的电子行为.

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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.
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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.
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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 Hückel’s rule or the 4n +...
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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...
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