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Related Concept Videos

Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-Membered Heterocyclic Aromatic Compounds: Overview

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

Criteria for Aromaticity and the Hückel 4n + 2 Rule

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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 +...
15.1K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

4.4K
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...
4.4K
Basicity of Heterocyclic Aromatic Amines01:25

Basicity of Heterocyclic Aromatic Amines

7.2K
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).
7.2K
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

4.3K
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.
4.3K
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

2.9K
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...
2.9K

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Hydrogen bond-aromaticity cooperativity in self-assembling 4-pyridone chains.

Megha Anand1, Israel Fernández2, Henry F Schaefer1

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

Journal of Computational Chemistry
|June 24, 2015
PubMed
Summary

Hydrogen bonding in 4-pyridone chains enhances π-aromaticity by polarizing bonds and increasing electron delocalization. This effect strengthens interactions and grows with chain length.

Keywords:
aromaticityenergy decomposition analysishydrogen bondingnucleus independent chemical shiftsself-assembly

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Area of Science:

  • Supramolecular Chemistry
  • Computational Chemistry
  • Organic Chemistry

Background:

  • 4-pyridone is a self-assembling building block with notable H-bond-aromaticity coupling.
  • Understanding these interactions is key to designing novel materials.

Purpose of the Study:

  • To investigate the impact of hydrogen bonding on the aromaticity of 4-pyridone chains.
  • To quantify the relationship between H-bonding and π-electron delocalization.

Main Methods:

  • Computational chemistry methods including nucleus independent chemical shifts (NICS(1)zz), natural bond orbital (NBO) charges, and energy decomposition analyses (EDA).
  • Systematic study of hydrogen-bonded 4-pyridone chains (4-py)n, where n ranges from 2 to 8.

Main Results:

  • Hydrogen bonding polarizes the exocyclic C=O bonds in 4-pyridone.
  • Increased π-electron delocalization (4n+2) within the six-membered ring was observed.
  • Enhanced π-aromatic character and strengthened N-H···O=C interactions were confirmed.
  • These effects increase with the number of H-bonded units, irrespective of orientation.

Conclusions:

  • Hydrogen bonding significantly enhances the π-aromatic character of 4-pyridone chains.
  • The findings provide insights into the interplay between non-covalent interactions and electronic properties in self-assembling systems.