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Understanding the planar tetracoordinate carbon atom: spiropentadiene dication
Caio L Firme1, Narciso B P Barreiro, Pierre M Esteves
1Universidade Federal do Rio de Janeiro, Instituto de Química, Av. Athos da Silveira Ramos 149, Cidade Universitária-Ilha do Fundão, Rio de Janeiro, Brazil.
The Journal of Physical Chemistry. A
|January 9, 2008
Summary
The spiropentadiene dication features a unique planar tetracoordinate carbon atom with a negative charge, stabilized by sigma bonds. This structure exhibits a low activation barrier for ring opening, indicating potential reactivity.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Organic Chemistry
Background:
- The study of unusual bonding in organic molecules is crucial for understanding chemical reactivity.
- Planar tetracoordinate carbon (ptC) centers are rare and theoretically challenging to stabilize.
- Spirodienes represent a class of compounds with unique structural and electronic properties.
Purpose of the Study:
- To investigate the electronic structure and stability of the spiropentadiene dication.
- To analyze the bonding characteristics of the planar tetracoordinate carbon atom within the dication.
- To determine the energetic barrier for ring opening in the spiropentadiene dication.
Main Methods:
- Ab initio electronic structure calculations were employed.
- Analysis of the molecular orbital theory was performed.
- Potential energy surface scans were conducted to identify reaction pathways.
Main Results:
- The spiropentadiene dication was found to possess a planar tetracoordinate carbon (ptC) atom.
- This ptC atom carries a net negative charge, stabilized primarily by sigma bonds.
- The bonds to the ptC atom exhibit reduced covalent character compared to neutral analogs, with the positive charge delocalized.
- A modest activation barrier of 2.3 kcal/mol was calculated for the ring-opening reaction.
Conclusions:
- The theoretical investigation confirms the existence and stability of the spiropentadiene dication with a ptC center.
- The electronic distribution and bonding in the dication are distinct from neutral counterparts.
- The low activation barrier suggests that the spiropentadiene dication is susceptible to ring-opening reactions.
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