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Aromatic Hydrocarbon Cations: Structural Overview

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...

Thermal and Photochemical Electrocyclic Reactions: Overview

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.

Nomenclature of Alkynes

Nomenclature of Alkynes

Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes:

Structure of Conjugated Dienes

Structure of Conjugated Dienes

Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...

Thermal Electrocyclic Reactions: Stereochemistry

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.

Stability of Conjugated Dienes

Stability of Conjugated Dienes

Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.

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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

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Persistent peri-Heptacene: Synthesis and In Situ Characterization.

M R Ajayakumar¹, Ji Ma¹, Andrea Lucotti²

¹Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, 01062, Dresden, Germany.

Angewandte Chemie (International Ed. in English)

|April 13, 2021

Summary

Researchers synthesized peri-heptacene (7-PA), a novel graphene nanoribbon model, overcoming challenges of open-shell character. This breakthrough enables future applications in nanoelectronics and spintronics.

Keywords:

Scholl reaction acenes graphene nanostructures radicals

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Published on: September 18, 2016

Area of Science:

Materials Science
Organic Chemistry
Nanotechnology

Background:

n-peri-Acenes (n-PAs) are model systems for zigzag-edged graphene nanoribbons.
Synthesis of larger n-PAs is hindered by open-shell character and reactivity.

Purpose of the Study:

To synthesize a novel, larger n-PA, specifically peri-heptacene (7-PA).
To overcome synthetic challenges associated with reactive zigzag edges in n-PAs.

Main Methods:

Kinetic protection of reactive zigzag edges using 4-tBu-C6H4 groups.
Validation of synthesis via high-resolution mass spectrometry and in situ FT-Raman spectroscopy.
Characterization using electron-spin resonance and theoretical studies.

Main Results:

Successful synthesis and characterization of peri-heptacene (7-PA).
7-PA exhibits a narrow optical energy gap (1.01 eV) and persistent stability (t1/2 ≈25 min).
Demonstrated open-shell character and significant tetraradical nature.

Conclusions:

A modular strategy for synthesizing next-generation (3N+1)-PAs is presented.
This work advances the potential of n-PAs in nanoelectronics and spintronics.
Kinetic protection is a viable approach for stabilizing reactive PA structures.