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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Polycyclic benzenoids: why kinked is more stable than straight.
Jordi Poater1, Ruud Visser, Miquel Solà
1Afdeling Theoretische Chemie, Scheikundig Laboratorium der Vrije Universiteit, De Boelelaan 1083, NL-1081 HV Amsterdam, The Netherlands.
The Journal of Organic Chemistry
|February 10, 2007
Summary
Bent polycyclic benzenoids like phenanthrene are more stable than linear ones. This study shows their enhanced stability arises from pi-electron system bonding, not H-H interactions, challenging existing theories.
Area of Science:
- Physical Chemistry
- Theoretical Chemistry
- Organic Chemistry
Background:
- The enhanced stability of kinked polycyclic benzenoids (e.g., phenanthrene) over linear isomers (e.g., anthracene) is known but debated.
- A recent hypothesis attributes phenanthrene's stability to stabilizing H-H interactions in the bay region, contradicting steric repulsion evidence.
Purpose of the Study:
- To investigate the origin of enhanced stability in kinked polycyclic benzenoids compared to linear ones.
- To re-evaluate the role of hydrogen-hydrogen interactions in the bay region of phenanthrene.
- To test the validity of the theory of atoms-in-molecules (AIM) in interpreting bonding interactions.
Main Methods:
- Quantitative energy decomposition analysis (EDA) of the bonding between molecular fragments.
- Comparative analysis of phenanthrene, anthracene, hexacene, and its bent isomers.
- Application of the theory of atoms-in-molecules (AIM) and analysis of bond paths and critical points.
Main Results:
- Evidence confirms repulsive, not stabilizing, H-H interactions in phenanthrene's bay region.
- Enhanced stability of phenanthrene is attributed to more efficient pi-electron system bonding.
- AIM bond paths and critical points between bay hydrogens in phenanthrene indicate proximity, not necessarily stabilization.
Conclusions:
- The H-H interactions in phenanthrene's bay region are repulsive, refuting the stabilizing H-H bonding hypothesis.
- Efficient pi-electron bonding is the primary source of enhanced stability in kinked polycyclic benzenoids.
- AIM bond critical points do not solely indicate stabilizing interactions; they reflect charge distribution proximity, which can be repulsive.
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