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Related Concept Videos

Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

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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...
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Conformations of Cyclohexane02:11

Conformations of Cyclohexane

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Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
15.0K
Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

17.7K
The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
17.7K
Conformations of Cycloalkanes02:29

Conformations of Cycloalkanes

13.9K
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...
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π Molecular Orbitals of 1,3-Butadiene01:24

π Molecular Orbitals of 1,3-Butadiene

11.1K
Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
11.1K
Newman Projections02:06

Newman Projections

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Different notations are used to represent the three-dimensional structure of molecules on two-dimensional surfaces. One of the most commonly used representations is the dash-wedge formula. The dashed wedges, solid wedges, and the plane lines indicate the groups situated behind the plane, coming out of the plane, and in the plane, respectively.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as...
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A pentacene with a 144 degrees twist.

Jun Lu1, Douglas M Ho, Nancy J Vogelaar

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

Journal of the American Chemical Society
|September 10, 2004
PubMed
Summary

Researchers synthesized a highly twisted polycyclic aromatic hydrocarbon, 9,10,11,20,21,22-Hexaphenyltetrabenzo[a,c,l,n]pentacene. Its unique structure exhibits significant twisting, and its enantiomers show high optical rotation but undergo slow racemization.

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Supramolecular Chemistry

Background:

  • Polycyclic aromatic hydrocarbons (PAHs) are crucial in materials science.
  • Understanding molecular twisting is key to designing novel functional materials.
  • Highly twisted PAHs present unique structural and electronic properties.

Purpose of the Study:

  • To synthesize and characterize a novel, highly twisted polycyclic aromatic hydrocarbon.
  • To investigate the structural and chiroptical properties of the synthesized compound.
  • To explore the racemization dynamics of the chiral molecule.

Main Methods:

  • Synthesis via reaction of 1,3-diphenylphenanthro[9,10-c]furan with a bisaryne equivalent.
  • Deoxygenation of the double adduct using low-valent titanium.
  • X-ray crystallography for structural determination.
  • Chiral chromatography for enantiomeric separation.
  • Polarimetry to measure specific rotations.
  • Racemization studies at room temperature.

Main Results:

  • Successful synthesis of 9,10,11,20,21,22-Hexaphenyltetrabenzo[a,c,l,n]pentacene (1).
  • X-ray structure reveals compound 1 as the most highly twisted polycyclic aromatic hydrocarbon known (143.6 degrees end-to-end twist).
  • Pure enantiomers of compound 1 exhibit high specific rotations (>7000 degrees).
  • Compound 1 undergoes slow racemization at 25°C with a half-life of 9.3 hours.

Conclusions:

  • 9,10,11,20,21,22-Hexaphenyltetrabenzo[a,c,l,n]pentacene represents a new benchmark in molecular twisting for PAHs.
  • The molecule's chirality and racemization dynamics offer insights into stereochemistry in strained systems.
  • This study expands the scope of complex PAH synthesis and characterization.