Stabilizing 4π electron pyrrolyl cations by inducing aromaticity
Astha Gupta1, Mohammad Ovais Dar1,2, Tejender Singh1
1National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S.A.S. Nagar-160062, Punjab, India. pvbharatam@niper.ac.in.
Chemical Communications (Cambridge, England)
|November 29, 2024
Summary
Researchers created stable pyrrolyl cations, which are typically unstable anti-aromatic compounds. This was achieved by using N-heterocyclic carbenes to convert the 4π electron system into a stable 6π electron system.
Area of Science:
- Organic Chemistry
- Aromaticity Studies
Background:
- Pyrrolyl cations are inherently unstable 4π electron ring systems.
- Anti-aromaticity leads to significant energetic destabilization.
Purpose of the Study:
- To develop an experimental method for synthesizing stable pyrrolyl cations.
- To investigate stabilization mechanisms for anti-aromatic species.
Main Methods:
- Utilized N-heterocyclic carbenes as stabilizing agents.
- Employed experimental procedures for cation generation and characterization.
Main Results:
- Successfully obtained stable pyrrolyl cations under experimental conditions.
- Demonstrated the conversion of a 4π electron system to a 6π electron system.
- N-heterocyclic carbenes were shown to stabilize the pyrrolyl cation through electron donation.
Conclusions:
- N-heterocyclic carbenes effectively stabilize otherwise unstable pyrrolyl cations.
- This work provides a pathway to access and study novel aromatic systems.
More Related Videos
![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)
Related Concept Videos
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
2.7K
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...
2.7K
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
10.3K
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...
10.3K
01:13Five-Membered Heterocyclic Aromatic Compounds: Overview
3.8K
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,...
3.8K