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Related Concept Videos

Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic factors, steric factors also account...
ortho–para-Directing Deactivators: Halogens01:24

ortho–para-Directing Deactivators: Halogens

Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)01:30

Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)

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 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...
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
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...

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Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates
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TABF as a Double Proton Sponge: Steric Preorganization versus Antiaromatic Destabilization.

Julien F Rowen1, Yining Liu2, Maurice Niehoff1

  • 1Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, Bochum 47780, Germany.

The Journal of Organic Chemistry
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PubMed
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Researchers synthesized a new proton sponge, 1,1

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Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates
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Area of Science:

  • Organic Chemistry
  • Supramolecular Chemistry

Background:

  • Proton sponges are organic molecules with high basicity.
  • Their basicity depends on molecular structure.
  • 1,8-bis(dimethylamino)naphthalene (DMAN) is a common proton sponge.

Purpose of the Study:

  • To synthesize a novel proton sponge scaffold, 1,1',8,8'-tetraazabifluorenylidene (TABF).
  • To investigate the acid-base properties and structural characteristics of TABF.
  • To understand the relationship between molecular architecture and basicity in proton sponges.

Main Methods:

  • Synthesis of the TABF scaffold.
  • Single-crystal X-ray diffraction to determine molecular structures.
  • UV-vis spectrophotometric titrations in acetonitrile to determine acid-base properties.

Main Results:

  • The synthesis of TABF was successful.
  • X-ray diffraction confirmed the structures of the neutral base and the dication.
  • Spectrophotometric titrations yielded pKaH,2 = 15.0-15.6 and pKaH,1 ≈ 18.
  • TABF exhibits lower basicity than DMAN.

Conclusions:

  • TABF is a novel proton sponge with tunable basicity.
  • The reduced basicity is due to antiaromatic destabilization in protonated forms.
  • Electronic structure and charge distribution are crucial for designing organic superbases.