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Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
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Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
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Dynamic Covalent Spiropyran Exchange for Rapid Structural Diversification.

Alwin Drichel1,2, Yves Garmshausen3, Stefan Hecht4,5,1,2

  • 1DWI-Leibniz Institute for Interactive Materials, Forckenbeckstr. 50, 52074, Aachen, Germany.

Angewandte Chemie (International Ed. in English)
|January 2, 2025
PubMed
Summary
This summary is machine-generated.

Spiropyrans can dynamically exchange structures via their merocyanine forms. This dynamic covalent exchange, catalyzed by indolinium salts, allows for rapid structural diversification and synthesis of novel spiropyrans for applications like photoinitiators.

Keywords:
Dynamic Covalent ChemistryMerocyanineSpiropyranXolography

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Area of Science:

  • Organic Chemistry
  • Materials Science
  • Polymer Chemistry

Background:

  • Spiropyrans are photochromic compounds known for their reversible structural transformations.
  • Dynamic covalent chemistry offers pathways for adaptive materials and molecular assembly.
  • Controlling spiropyran structures is crucial for tuning their photochromic and material properties.

Purpose of the Study:

  • To disclose and characterize the dynamic covalent exchange of spiropyrans through their merocyanine isomers.
  • To investigate the mechanism and influencing factors of spiropyran cross-exchange.
  • To utilize this exchange for the synthesis of novel spiropyran derivatives and explore their applications.

Main Methods:

  • Investigated spiropyran dynamic covalent exchange via merocyanine intermediates.
  • Analyzed the Michael-type addition-elimination sequence for indolinium moiety exchange.
  • Studied the effect of reaction conditions and substituent patterns on exchange equilibrium.
  • Employed indolinium salts as catalysts for spiropyran cross-exchange.

Main Results:

  • Demonstrated that spiropyrans undergo dynamic covalent exchange facilitated by merocyanine isomers.
  • Identified the Michael-type addition-elimination sequence as the key exchange mechanism.
  • Showcased the synthesis of previously inaccessible spiropyrans using this method, suitable for dual-color photoinitiators in xolography.
  • Established that exchange rate and equilibrium are tunable via reaction conditions and molecular structure.

Conclusions:

  • Spiropyran dynamic covalent exchange is a viable strategy for in situ structural diversification.
  • This methodology enables access to novel spiropyran architectures with potential applications in advanced materials.
  • The light-sensitivity of spiropyrans can be exploited to control and bias their thermal equilibrium in dynamic systems.