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Related Concept Videos

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

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

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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...
2.0K
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

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

7.8K
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...
7.8K
Five-Membered Heterocyclic Aromatic Compounds: Overview01:13

Five-Membered Heterocyclic Aromatic Compounds: Overview

5.9K
Heterocyclic aromatic compounds are cyclic compounds that are aromatic and have one or more heteroatoms—atoms other than carbon, in the ring. Depending upon the number of atoms present in the ring, they can be either five or six-membered. Examples of five-membered heterocyclic aromatic compounds include pyrrole, furan, thiophene, and imidazole. Pyrrole consists of one nitrogen atom having one lone pair of electrons. Furan and thiophene have one oxygen and one sulfur heteroatom,...
5.9K
Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

4.1K
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...
4.1K
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

4.0K
The inscribed polygon method is consistent with Hückel’s 4n + 2 rule and helps to learn whether the given cyclic compound is aromatic or not. The compound is stable and aromatic if every bonding molecular orbital (MO) is completely filled with a pair of electrons. However, if the non-bonding or antibonding orbitals are filled with electrons, the compound is unstable and not aromatic. Consider the Frost circle diagrams for cycloalkenes containing 4 to 8 carbons.
4.0K
NMR Spectroscopy of Aromatic Compounds01:14

NMR Spectroscopy of Aromatic Compounds

6.6K
Aromatic compounds can be identified or analyzed using proton NMR and carbon‐13 NMR. Typically, aromatic hydrogens or hydrogens directly bonded to the aromatic rings are strongly deshielded by the aromatic ring current. Therefore, they absorb in the range of 6.5–8.0 ppm in proton NMR spectra. For instance, aromatic hydrogens directly bonded to the benzene ring absorb at 7.3 ppm. However, aromatic hydrogens of larger rings absorb farther upfield or downfield than the ideal range.
6.6K

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Related Experiment Video

Updated: Mar 6, 2026

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
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New complexity for aromatic ring agostic interactions.

M Arif Sajjad1, Kirsten E Christensen, Nicholas H Rees

  • 1Chemistry, Institute of Natural and Mathematical Sciences, Massey University Auckland, Private Bag 102904, North Shore Mail Centre, Auckland, New Zealand. a.j.nielson@massey.ac.nz.

Chemical Communications (Cambridge, England)
|March 14, 2017
PubMed
Summary
This summary is machine-generated.

Density functional theory (DFT) calculations show agostic donation and pi-donation share orbitals during aromatic C-H bond activation. This finding impacts understanding of C-H activation chemistry.

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Area of Science:

  • Organometallic Chemistry
  • Computational Chemistry

Background:

  • Ligand-directed C-H bond activation is crucial in synthetic chemistry.
  • Understanding the electronic factors governing these reactions is key.

Purpose of the Study:

  • To investigate the electronic interactions during ligand-directed aromatic C-H bond activation.
  • To elucidate the role of agostic and pi-donations in this process.

Main Methods:

  • Utilized Density Functional Theory (DFT) calculations.
  • Analyzed orbital interactions in catalytic cycles.

Main Results:

  • Agostic donation and pi-donation from the aromatic ligand utilize shared antibonding acceptor orbitals.
  • Identified previously unrecognized pi-donation from the ligand's aromatic ring.

Conclusions:

  • The interaction of carbon-based orbitals significantly influences agostic interactions.
  • This discovery has substantial implications for advancing C-H bond activation strategies.