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Related Concept Videos

Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria 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 Hückel’s rule or...
10.3K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.4K
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
2.4K
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

3.2K
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.
3.2K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

3.4K
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...
3.4K
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

3.4K
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...
3.4K
Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

5.8K
Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).
5.8K

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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

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Reciprocal hydrogen bonding-aromaticity relationships.

Judy I Wu1, James E Jackson, Paul von Ragué Schleyer

  • 1Center for Computational Quantum Chemistry, University of Georgia , Athens, Georgia 30602, United States.

Journal of the American Chemical Society
|September 13, 2014
PubMed
Summary

Hydrogen bonding significantly impacts molecular aromaticity, with increased electron delocalization boosting interactions. Conversely, decreased aromaticity weakens these bonds, influencing chemical behavior.

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Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates
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Area of Science:

  • Computational chemistry
  • Physical organic chemistry
  • Quantum chemistry

Background:

  • Aromaticity is a key concept in chemistry, influencing molecular stability and reactivity.
  • Hydrogen bonding is a crucial intermolecular force affecting molecular interactions and properties.
  • The interplay between aromaticity and hydrogen bonding in conjugated systems is not fully understood.

Purpose of the Study:

  • To investigate the mutual influence of hydrogen bonding and aromaticity in π-conjugated systems.
  • To quantify the impact of intermolecular interactions on aromaticity and vice versa.
  • To explore the role of these effects in tautomeric equilibria of heterocyclic compounds.

Main Methods:

  • Computed association energies using quantum chemical methods.
  • Dissected nucleus-independent chemical shifts (NICS) to assess aromaticity.
  • Theoretical modeling of H-bonded complexes and tautomeric equilibria.

Main Results:

  • Hydrogen bonding that enhances π-electron delocalization increases aromaticity.
  • Decreased aromaticity, due to quinoidal π character, weakens hydrogen bonding interactions.
  • The study provides quantitative evidence for the H-bonding/aromaticity interplay.

Conclusions:

  • Hydrogen bonding and aromaticity are intrinsically linked in π-conjugated systems.
  • This interplay significantly affects molecular properties and chemical behavior, including tautomerism.
  • Understanding this relationship is crucial for designing and predicting the behavior of organic molecules.