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Related Concept Videos

Electrophilic Aromatic Substitution: Overview01:16

Electrophilic Aromatic Substitution: Overview

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In an electrophilic aromatic substitution reaction, an electrophile substitutes for a hydrogen of an aromatic compound.
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π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

1.2K
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...
1.2K
Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)01:30

Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)

3.9K
Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between...
3.9K
Basicity of Aromatic Amines01:18

Basicity of Aromatic Amines

7.2K
The basicity of aromatic amines is much weaker than that of aliphatic amines due to the involvement of the lone pair of electrons over the N atom in resonance with the aryl rings. Generally, the electron-donating ability of any substituents on the aryl ring of aromatic amines increases the basicity of the amine by increasing electron density, and hence the availability of lone pair on the nitrogen. On the other hand, electron-withdrawing functional groups on the aryl ring of amines decrease the...
7.2K
Nucleophilic Aromatic Substitution: Elimination–Addition01:11

Nucleophilic Aromatic Substitution: Elimination–Addition

4.0K
Simple aryl halides do not react with nucleophiles. However, nucleophilic aromatic substitutions can be forced under certain conditions, such as high temperatures or strong bases. The mechanism of substitution under such conditions involves the highly unstable and reactive benzyne intermediate. Benzyne contains equivalent carbon centers at both ends of the triple bond, each of which is equally susceptible to nucleophilic attack. This 50–50 distribution of products is...
4.0K
Substituent Effects on Acidity of Carboxylic Acids01:31

Substituent Effects on Acidity of Carboxylic Acids

6.9K
The acidity of carboxylic acids is influenced by the nature of the substituents bounded to the functional group. The acid strength is determined by the stability of the carboxylate anion—the conjugate base formed by dissociating the corresponding carboxylic acid.
6.9K

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Related Experiment Video

Updated: Jul 26, 2025

Efficient Synthesis of Polyfunctionalized Benzenes in Water via Persulfate-promoted Benzannulation of &#945;,&#946;-Unsaturated Compounds and Alkynes
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Substituent effects on aromatic interactions in water.

Gloria Tobajas-Curiel1, Qingqing Sun2,3, Jeremy K M Sanders1

  • 1Yusuf Hamied Department of Chemistry, University of Cambridge Cambridge CB2 1EW UK herchelsmith.orgchem@ch.cam.ac.uk.

Chemical Science
|June 16, 2023
PubMed
Summary

Molecular recognition in water is complex, but well-defined supramolecular complexes reveal key factors. Substituents on guest molecules significantly enhance binding affinity through entropic contributions from desolvation.

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Controlling the Size, Shape and Stability of Supramolecular Polymers in Water
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Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

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Area of Science:

  • Supramolecular Chemistry
  • Physical Organic Chemistry
  • Molecular Recognition

Background:

  • Molecular recognition in water is challenging due to complex interactions like desolvation and conformational changes.
  • Studying well-defined supramolecular complexes in different solvents aids in dissecting these contributions.
  • Calix[4]pyrrole receptors and pyridine N-oxide guests form stable complexes suitable for such studies.

Purpose of the Study:

  • To dissect the factors governing substituent effects on aromatic interactions in water using calix[4]pyrrole-pyridine N-oxide complexes.
  • To quantify the thermodynamic contribution of aromatic interactions and substituent effects on complex stability.
  • To compare substituent effects in water with those in non-polar solvents like chloroform.

Main Methods:

  • Formation of 1:1 complexes between four calix[4]pyrrole receptors and thirteen pyridine N-oxide guests.
  • Quantification of thermodynamic contributions using chemical double mutant cycles.
  • Experimental techniques included isothermal titration calorimetry and 1H NMR competition experiments.

Main Results:

  • Aromatic interactions between receptor and guest phenyl groups stabilize complexes by a factor of 1000.
  • Substituents on the guest phenyl group further enhance stability by up to 1000-fold, with a nitro substituent yielding a 370 fM dissociation constant.
  • Enhanced substituent effects in water are attributed to favorable entropic contributions from desolvation of hydrophobic surfaces.

Conclusions:

  • Flexible receptor structures facilitate desolvation of polar substituents, maximizing non-polar interactions with the receptor and polar interactions with the solvent.
  • These optimized interactions lead to remarkably high binding affinities in aqueous media.
  • Electrostatic interactions play a significant role, particularly in non-polar solvents, while entropic effects dominate in water.