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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...
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...
Radicals: Electronic Structure and Geometry01:07

Radicals: Electronic Structure and Geometry

This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...

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Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Published on: September 18, 2016

Functionalized thiophene-based [7]helicene: chirooptical properties versus electron delocalization.

Andrzej Rajca1, Maren Pink, Shuzhang Xiao

  • 1Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, USA. arajca1@unl.edu

The Journal of Organic Chemistry
|September 11, 2009
PubMed
Summary

A new enantiomerically pure [7]helicene was synthesized from a bis(benzodithiophene) building block. Its chirooptical properties were similar to related helicenes, suggesting electron delocalization has minimal impact on these properties.

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Published on: September 26, 2016

Area of Science:

  • Organic Chemistry
  • Materials Science
  • Supramolecular Chemistry

Background:

  • Helicenes are chiral polycyclic aromatic hydrocarbons with unique electronic and optical properties.
  • Functionalized helicenes serve as building blocks for advanced materials and molecular devices.
  • Sulfur-containing heterocycles offer tunable electronic characteristics compared to their all-carbon counterparts.

Purpose of the Study:

  • To synthesize a novel enantiomerically pure [7]helicene incorporating a bis(benzodithiophene) core.
  • To investigate the chirooptical properties and electron delocalization of the synthesized [7]helicene.
  • To establish a correlation between chirooptical properties and electron delocalization in a series of [7]helicenes.

Main Methods:

  • Synthesis of a functionalized bis(benzodithiophene) building block (2).
  • Preparation of enantiomerically pure [7]helicene 1 from building block 2.
  • Characterization of chirooptical properties and electron delocalization.
  • Single-crystal X-ray analysis of [7]helicene 1 and building block 2.

Main Results:

  • Successful synthesis of enantiomerically pure [7]helicene 1 with a bis(benzodithiophene) core and solubilizing heptyl groups.
  • Moderately increased electron delocalization in [7]helicene 1 compared to analogous structures.
  • Similar chirooptical properties observed between [7]helicene 1 and related helicenes with lower electron delocalization.
  • X-ray analysis confirmed the molecular structures and revealed chiral, needle-like crystals for the building block.

Conclusions:

  • Chirooptical properties of this series of [7]helicenes are not significantly influenced by the degree of electron delocalization.
  • [7]Helicene 1 is a promising building block for constructing longer helicene structures and oligomers.
  • The study provides valuable insights into structure-property relationships in functionalized helicenes.