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

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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...
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Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
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Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
8.2K
Cycloaddition Reactions: MO Requirements for Photochemical Activation01:12

Cycloaddition Reactions: MO Requirements for Photochemical Activation

2.0K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
2.0K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
1.8K
Aldehydes and Ketones with Amines: Imine Formation Mechanism01:23

Aldehydes and Ketones with Amines: Imine Formation Mechanism

5.1K
Imine formation involves the addition of carbonyl compounds to a primary amine. It begins with the generation of carbinolamine through a series of steps involving an initial nucleophilic attack and then several proton transfer reactions. The second part includes the elimination of water, as a leaving group, to give the imine.
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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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Visible-Light Switchable Rings and Chains in Dynamic Covalent Imine Chemistry.

Jona Voss1,2, Yannic Hartmann1, Esther Nieland1

  • 1Institut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, Düsseldorf, Germany.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|March 27, 2025
PubMed
Summary
This summary is machine-generated.

Red-light switchable azobenzene isomers form distinct macrocycles with diamines. Chain length dictates self-assembly, enabling control over photoresponsive materials via dynamic covalent chemistry.

Keywords:
aldehydesaminesmacrocyclesphotochemistrysupramolecular chemistry

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Area of Science:

  • Supramolecular Chemistry
  • Organic Chemistry
  • Materials Science

Background:

  • Azobenzene derivatives are photoresponsive molecules with tunable properties.
  • Self-assembly of functionalized molecules offers pathways to complex structures.
  • Dynamic covalent chemistry utilizes reversible reactions for adaptive materials.

Purpose of the Study:

  • To investigate the self-assembly of red-light switchable ortho-difluoroazobenzene isomers with aliphatic diamines.
  • To understand the influence of diamine chain length on macrocycle formation and photoresponsiveness.
  • To explore the potential of these systems in dynamic covalent chemistry and adaptive materials.

Main Methods:

  • Synthesis of functionalized ortho-difluoroazobenzene isomers (E-/Z-A).
  • Reaction with various aliphatic diamines (e.g., propane-1,3-diamine, butane-1,4-diamine).
  • Characterization using single-crystal X-ray diffraction, 19F-DOSY NMR, MALDI-MS, and UV/Vis spectroscopy.

Main Results:

  • Self-assembly exhibits alternating behavior based on diamine chain length (odd vs. even).
  • Even-numbered diamines exclusively form imine macrocycles with the Z-azobenzene isomer.
  • Odd-numbered diamines form photoswitchable, defined macrocycles, including E,E-A2X2 types, confirmed by X-ray structures.

Conclusions:

  • Diamine conformation, influenced by methylene group count, dictates reactivity and self-assembly outcomes.
  • Precise control over macrocycle structure and photoresponsive properties is achievable.
  • Azobenzene-based systems offer significant potential for developing advanced adaptive materials.