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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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Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

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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.
Due to the absence of continuous...
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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
NMR Spectroscopy of Aromatic Compounds01:14

NMR Spectroscopy of Aromatic Compounds

4.7K
Aromatic compounds can be identified or analyzed using proton NMR and carbon‐13 NMR. Typically, aromatic hydrogens or hydrogens directly bonded to the aromatic rings are strongly deshielded by the aromatic ring current. Therefore, they absorb in the range of 6.5–8.0 ppm in proton NMR spectra. For instance, aromatic hydrogens directly bonded to the benzene ring absorb at 7.3 ppm. However, aromatic hydrogens of larger rings absorb farther upfield or downfield than the ideal range.
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Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria for Aromaticity and the Hückel 4n + 2 Rule

10.5K
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...
10.5K
Aromatic Compounds: Overview01:25

Aromatic Compounds: Overview

11.7K
In general, the term ‘aromatic’ indicates a pleasant smell or fragrance from fresh flowers, freshly prepared coffee, etc. In the early history of organic chemistry, many benzene derivatives were isolated from the pleasant odor oils of the plants. For example, vanillin was isolated from the oil of vanilla, methyl salicylate from the oil of wintergreen, and cinnamaldehyde from the oil of cinnamon. They all had a pleasant odor; hence the name aromatic was given.
In 1825, Faraday...
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Related Experiment Video

Updated: Apr 27, 2026

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
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What does the aromatic ring number mean for drug design?

Simon E Ward1, Paul Beswick

  • 1University of Sussex, Translational Drug Discovery Group , Brighton, East Sussex, BN1 9QJ , UK +44 1273 876659 ; Simon.Ward@sussex.ac.uk.

Expert Opinion on Drug Discovery
|June 24, 2014
PubMed
Summary

Drug developability is influenced by aromatic ring count. While molecules with more than three aromatic rings are generally undesirable, current research is limited by the diversity of compounds analyzed.

Keywords:
aromatic ringchemical spacedevelopabilityheteroaliphatic ringheteroaromatic ringlipophilicitysolubility

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Area of Science:

  • Medicinal Chemistry
  • Drug Discovery
  • Chemical Biology

Background:

  • Increased focus on factors influencing drug development success.
  • Aromatic ring count identified as a key factor in drug developability.
  • Growing body of literature exploring the impact of aromaticity in drug design.

Purpose of the Study:

  • To review the literature on the consequences of aromatic rings in drug molecules.
  • To analyze the influence of aromatic ring count on compound developability.
  • To discuss implications for medicinal chemists and limitations of current analyses.

Main Methods:

  • Comprehensive literature review of recent publications.
  • Analysis of positive and negative consequences of aromatic rings.
  • Evaluation of studies on aromatic ring count and developability.

Main Results:

  • Drug molecules with >3 aromatic rings are generally considered undesirable.
  • Heteroaromatic compounds demonstrate better developability compared to carboaromatic compounds.
  • Current analyses are limited by the restricted diversity of compound collections, particularly those designed for oral administration.

Conclusions:

  • Medicinal chemists operate within a constrained chemical space.
  • Safe drug candidates may exist outside conventional drug-like chemical space.
  • Further research with diverse compound libraries is needed to fully understand the role of aromatic rings in drug developability.