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Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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The [12]annulene global minimum.

Miles N Braten1, Claire Castro, Rainer Herges

  • 1Department of Chemistry, University of San Francisco, 2130 Fulton Street, San Francisco, California 94117, USA.

The Journal of Organic Chemistry
|January 18, 2008
PubMed
Summary
This summary is machine-generated.

A novel, more stable isomer of [12]annulene, designated mono-trans (CCCCCT), has been discovered computationally. Its stability and predicted low rearrangement barriers suggest experimental characterization is feasible.

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Area of Science:

  • Organic Chemistry
  • Computational Chemistry
  • Theoretical Chemistry

Background:

  • [12]annulene is a non-benzenoid aromatic hydrocarbon with various known isomers.
  • Understanding the conformational landscape and relative stability of annulene isomers is crucial for predicting their chemical behavior.

Purpose of the Study:

  • To computationally locate and characterize new global minimum energy structures of [12]annulene.
  • To compare the stability of the newly found isomer with previously known isomers.
  • To assess the feasibility of experimental characterization by calculating relevant energy barriers.

Main Methods:

  • High-level ab initio electronic structure calculations were employed.
  • The coupled-cluster singles doubles with perturbative triples (CCSD(T)) method with a correlation-consistent polarized valence double-zeta (cc-pVDZ) basis set was used for energy refinement.
  • The B3LYP hybrid density functional (BHHLYP) with a 6-311+G** basis set was used for geometry optimization.

Main Results:

  • A new global minimum for [12]annulene, the mono-trans isomer (CCCCCT), was identified.
  • This mono-trans isomer is computationally predicted to be 1.5 kcal/mol more stable than the tri-trans isomer and 2.4 kcal/mol more stable than the di-trans isomer.
  • Calculated barriers for rearrangements of the mono-trans isomer exceed 15 kcal/mol, indicating kinetic stability.

Conclusions:

  • The mono-trans isomer of [12]annulene represents a new, highly stable structure.
  • The computed kinetic stability and predicted NMR shifts suggest that experimental characterization of this isomer is achievable.
  • Further computational studies on dynamic processes and NMR properties will aid in its definitive identification.