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Related Concept Videos

Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

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 with both...
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

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

Criteria for Aromaticity and the Hückel 4n + 2 Rule

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 + 2 rule.
Conformations of Cycloalkanes02:29

Conformations of Cycloalkanes

Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3  hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that was based on the...
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

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 overlap of p...
Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-Membered Heterocyclic Aromatic Compounds: Overview

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, respectively.

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Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives
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Published on: February 7, 2017

Configurationally stable longitudinally twisted polycyclic aromatic compounds.

Robert S Walters1, Christina M Kraml, Neal Byrne

  • 1Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.

Journal of the American Chemical Society
|November 13, 2008
PubMed
Summary
This summary is machine-generated.

Researchers developed new methods to synthesize stable, twisted polycyclic aromatic compounds. These compounds exhibit unique optical properties, including circularly polarized luminescence, with potential applications in advanced materials.

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Spectroscopy

Background:

  • Developing configurationally stable twisted polycyclic aromatic compounds (PACs) is challenging.
  • Controlling the twist direction and achieving stable chiral forms is crucial for their optical properties.

Purpose of the Study:

  • To synthesize configurationally stable twisted PACs using two distinct strategies.
  • To resolve and characterize the enantiomers of these novel twisted PACs and their metal complexes.

Main Methods:

  • Synthesis of dissymmetrically substituted PACs with naphthyl groups.
  • Chiral separation of isomers using preparative supercritical fluid chromatography (SFC) and high-performance liquid chromatography (HPLC).
  • Computational studies and spectroscopic analysis (circular dichroism, circularly polarized luminescence).

Main Results:

  • Successfully synthesized and resolved enantiomers of twisted PACs like 2,3-Bis(1-naphthyl)-1,4-diphenyltriphenylene (7) and 10-(1-naphthyl)-9,11,12,14-tetraphenylbenzo[b]triphenylene (13).
  • Observed moderately large specific rotations for 7 and unexpectedly small rotations for 13, explained by computational analysis of conformations.
  • Prepared a chiral iridium(III) complex (4) with a twisted ligand, which was configurationally stable but difficult to resolve preparatively due to solubility issues.

Conclusions:

  • The developed synthetic strategies enable the creation of configurationally stable, twisted PACs and their chiral derivatives.
  • These compounds exhibit significant chiroptical properties, including circular dichroism and circularly polarized luminescence.
  • Further research is needed to overcome solubility limitations for preparative resolution of certain metal complexes.