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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Tautomerism in Reduced Pyrazinacenes.
Roberto Scipioni1, Mauro Boero1, Gary J Richards1
1WPI Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan, Max Planck Institute for Polymer Research, Mainz, Ackermannweg 10, 55124, Germany, Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504 CNRS-University of Strasbourg, 23 rue du Loess, F-67034 Strasbourg, France, Computational Materials Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 Japan, and Fuel Cell Materials Center, Nanoionics Group, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan.
NH tautomerism in pyrazinacenes was investigated. Proton transfer lowers energy barriers and alters electronic structure, with stability influenced by proton position and molecular length, showing an odd-even effect.
Area of Science:
- Computational chemistry
- Organic electronics
- Supramolecular chemistry
Background:
- Oligoazaacenes, specifically pyrazinacenes, exhibit complex tautomeric behavior.
- Understanding NH tautomerism is crucial for predicting their electronic and structural properties.
Purpose of the Study:
- To investigate monoprotic and diprotic NH tautomerism in reduced pyrazinacenes.
- To elucidate the relationship between tautomerism, electronic structure, and molecular stability.
- To explore the influence of molecular length on tautomeric free energy profiles.
Main Methods:
- First principles simulations were employed.
- Metadynamics-sampled free energy profiles were calculated.
- Highest occupied molecular orbital (HOMO) structures were computed to analyze electronic contributions.
Main Results:
- Stepwise reductions in free energy barriers were observed during tautomerization.
- An unusual odd-even effect in free energy profiles was identified with increasing pyrazinacene length.
- Tautomers with central protons are more stable due to enhanced delocalization and reduced resonance stabilization.
Conclusions:
- Tautomerism significantly influences the electronic structure and stability of pyrazinacenes.
- Proton delocalization and molecular architecture dictate the observed tautomeric preferences.
- Computational findings are supported by experimental evidence of pyrazinacene tautomer structures.
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