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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

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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.
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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
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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.
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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.
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Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

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Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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Cationic Chain-Growth Polymerization: Mechanism00:57

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The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the...
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Pericyclic Reactions: Introduction01:17

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Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
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[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
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Reversible stimulus-responsive Cu(I) iodide pyridine coordination polymer.

P Amo-Ochoa1, K Hassanein, C J Gómez-García

  • 1Departamento de Química Inorgánica, Universidad Autónoma de Madrid, 28049 Madrid, Spain. felix.zamora@uam.es.

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|August 13, 2015
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Summary
This summary is machine-generated.

A flexible copper-iodide-pyridine material shows significant electrical conductivity changes with temperature and acetic acid sorption, enabling robust gas detection devices.

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Area of Science:

  • Materials Science
  • Chemistry
  • Nanotechnology

Background:

  • Coordination polymers offer tunable properties for advanced applications.
  • Developing novel materials for gas sensing is crucial for environmental and safety monitoring.

Purpose of the Study:

  • To investigate a flexible copper-iodide-pyridine coordination polymer.
  • To explore its electrical conductivity response to environmental stimuli.
  • To develop a gas detection device based on this material.

Main Methods:

  • Synthesis of a copper-iodide-pyridine-based coordination polymer.
  • Variable temperature electrical conductivity measurements.
  • Gas sorption studies with acetic acid.
  • X-ray diffraction analysis.
  • Density Functional Theory (DFT) calculations.

Main Results:

  • The coordination polymer exhibited drastic variations in electrical conductivity.
  • Conductivity was sensitive to temperature changes.
  • Sorption of acetic acid molecules significantly altered conductivity.
  • Structural flexibility was observed.
  • X-ray diffraction and DFT calculations provided insights into the observed phenomena.

Conclusions:

  • The studied material demonstrates significant potential for gas sensing applications.
  • Its tunable electrical properties make it suitable for fabricating simple and robust gas detection devices.
  • The interplay between structure, temperature, and guest molecule sorption dictates conductivity.