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Related Concept Videos

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

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In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
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Sigmatropic rearrangements are a class of pericyclic reactions in which a σ bond migrates from one part of a π system to another. These are intramolecular rearrangements where the total number of σ and π bonds remain unchanged.
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The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
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π Electron Effects on Chemical Shift: Overview01:27

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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,...
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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.
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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
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Strain-Driven Formal [1,3]-Aryl Shift within Molecular Bows.

Liang Jiang1,2, Zhen Peng2, Yimin Liang2

  • 1Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China.

Angewandte Chemie (International Ed. in English)
|September 1, 2023
PubMed
Summary
This summary is machine-generated.

Molecular strain engineering enables controlled aryl shifts in molecular bows, facilitating the formation of ortho-disubstituted products. This approach offers new synthetic strategies for precision organic synthesis.

Keywords:
Aryl ShiftCarbocation RearrangementMechanochemistryMolecular-Strain EngineeringStrained Structure

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Area of Science:

  • Organic Chemistry
  • Synthetic Chemistry
  • Physical Chemistry

Background:

  • Strain engineering in small molecules offers insights into reaction mechanisms.
  • Molecular bows (MBs) with 1,4-dimethoxy-2,5-cyclohexadiene moieties were investigated.
  • Understanding strain's influence is key for innovative synthetic strategies.

Purpose of the Study:

  • To present a molecular-strain engineering approach to facilitate consecutive aryl shifts.
  • To demonstrate the realization of a formal [1,3]-aryl shift through intramolecular strain.
  • To explore the application of molecular strain in precision organic synthesis.

Main Methods:

  • Introducing ring strain into MBs by tethering bow limbs.
  • Investigating the effect of solvent and temperature on aryl shifts.
  • Performing free energy calculations with solvation to support the mechanism.

Main Results:

  • Multistep aryl shifts from para- to meta- to ortho-positions were driven by intrinsic mechanical forces.
  • The formal [1,3]-aryl shift was achieved, yielding ortho-disubstituted products.
  • A feasible mechanism involving carbocation rearrangements was supported by calculations.

Conclusions:

  • Molecular strain engineering is a viable strategy for controlling complex organic reactions.
  • This research provides new tools and strategies for precision organic synthesis.
  • Harnessing mechanical forces in molecules opens avenues for designing compounds with superior properties.