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When disubstituted benzenes undergo electrophilic substitution, the product distribution depends on the directing effect of both substituents. When the directing effects of both substituents reinforce each other, a single product is obtained. For example, bromination of p-nitrotoluene occurs ortho to the methyl group and meta to the nitro group, which is the same position, resulting in a single product. However, if the directing effects of the two groups oppose each other, the...
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When more than one substituent is present on the benzene ring, the IUPAC nomenclature depends on the number of substituents present.
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Chlorination and bromination are important classes of electrophilic aromatic substitutions, where benzene reacts with chlorine or bromine in the presence of a Lewis acid catalyst to give halogenated substitution products. A Lewis acid such as aluminium chloride or ferric chloride catalyzes the chlorination, and ferric bromide catalyzes the bromination reactions. During the bromination of alkenes, bromine polarizes and becomes electrophilic. However, in the bromination of benzene, the bromine...
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In 1865, August Kekule suggested the structure of benzene according to the structural theory of organic chemistry based on the three assertions—formula of benzene is C6H6, all the hydrogens of benzene are equivalent, and each carbon must have four bonds due to its tetravalency.
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Multi PCET in symmetrically substituted benzimidazoles.

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Summary

Symmetrizing benzimidazole systems with two proton acceptors enables efficient two-proton transfer. This design ensures an uninterrupted hydrogen-bonded network, crucial for proton translocation in bioinspired constructs.

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Area of Science:

  • Supramolecular Chemistry
  • Bioinorganic Chemistry
  • Physical Chemistry

Background:

  • Proton-coupled electron transfer (PCET) is vital in biological systems, exemplified by the TyrZ-His190 pair in Photosystem II.
  • Benzimidazole (BIP) systems mimic natural PCET sites, facilitating studies of electron oxidation and proton transfer.
  • Challenges in PCET arise from isomers disrupting intramolecular hydrogen bonds, hindering efficient proton translocation.

Purpose of the Study:

  • To design and investigate a novel symmetrized benzimidazole system for enhanced two-proton translocation.
  • To overcome limitations posed by isomeric forms in monosubstituted systems.
  • To explore the role of hydrogen-bond connectivity in facilitating multiple proton transfers.

Main Methods:

  • Synthesis of disubstituted benzimidazole systems with identical terminal proton acceptors (TPAs).
  • Nuclear Magnetic Resonance (NMR) spectroscopy to analyze isomeric forms and hydrogen bonding.
  • Infrared spectroelectrochemistry to monitor proton transfer events and redox potentials.
  • Computational studies to elucidate structural and energetic properties.

Main Results:

  • A strategic symmetrization yielded a disubstituted system with an uninterrupted intramolecular hydrogen-bonded network, irrespective of isomeric form.
  • NMR confirmed a single isomer in the disubstituted system, unlike the monosubstituted analogue in specific solvents.
  • Infrared spectroelectrochemistry demonstrated efficient two-proton transfer at a lower redox potential in the disubstituted system.
  • Computational analysis revealed stabilization of the oxidized state via bifurcated hydrogen bonding.

Conclusions:

  • Symmetrized benzimidazole constructs with dual TPAs effectively facilitate two-proton transfer by maintaining a robust hydrogen-bonded network.
  • This design overcomes isomer-induced disruptions, enabling more reliable proton translocation.
  • The findings provide a foundation for developing advanced, bioinspired nanoscale proton transport systems.