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Related Concept Videos

Cycloaddition Reactions: MO Requirements for Thermal Activation01:16

Cycloaddition Reactions: MO Requirements for Thermal Activation

Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical example of a thermally-allowed cycloaddition is the Diels–Alder reaction, which is a [4 + 2] cycloaddition. In contrast, a [2 + 2] cycloaddition is thermally forbidden.
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

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.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
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...
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...
Cycloaddition Reactions: Overview01:16

Cycloaddition Reactions: Overview

Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
Frost Circles for Different Conjugated Systems01:18

Frost Circles for Different Conjugated Systems

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.

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Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Ions colliding with cold polycyclic aromatic hydrocarbon clusters.

A I S Holm1, H Zettergren, H A B Johansson

  • 1Department of Physics, Stockholm University, SE-106 91 Stockholm, Sweden.

Physical Review Letters
|January 15, 2011
PubMed
Summary
This summary is machine-generated.

Polycyclic aromatic hydrocarbon (PAH) clusters fragment more in ion collisions than other clusters. Surprisingly, heavier ions heat PAH clusters more effectively than lighter ions during these collisions.

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Area of Science:

  • Physical Chemistry
  • Chemical Physics
  • Materials Science

Background:

  • Polycyclic aromatic hydrocarbons (PAHs) are abundant in space and on Earth.
  • Understanding the behavior of PAH clusters is crucial for various scientific fields.
  • Previous studies have not experimentally investigated ion interactions with PAH clusters.

Purpose of the Study:

  • To conduct the first experimental study of ion interactions with polycyclic aromatic hydrocarbon (PAH) molecule clusters.
  • To investigate the fragmentation and heating dynamics of anthracene clusters upon ion impact.

Main Methods:

  • Experimental collisions using 11.25 keV 3He+ and 360 keV 129Xe20+ ions.
  • Utilizing weakly bound clusters of anthracene (C14H10) as the target material.
  • Analyzing fragmentation patterns and cluster heating through ion-molecule interactions.

Main Results:

  • Anthracene (C14H10) clusters exhibit a significantly higher tendency to fragment in ion collisions compared to other weakly bound clusters.
  • Ionization is predominantly driven by peripheral collisions.
  • Contrary to expectations, clusters were heated more intensely by Xe20+ collisions than by He+ collisions.
  • The observed appearance size for doubly charged anthracene clusters was k=15 for [C14H10](k)2+.

Conclusions:

  • PAH clusters possess unique fragmentation properties when subjected to ion impacts.
  • The energy transfer dynamics in ion-PAH cluster collisions are complex and depend on the projectile ion's characteristics.
  • These findings provide foundational insights into the physical and chemical processes involving PAH molecules in ionized environments.