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Computational study of isopropylbenzenium ions
1inGAP Center for Research Based Innovation, Department of Chemistry, University of Oslo, Blindern, Oslo, Norway. stein.kolboe@kjemi.uio.no
The Journal of Physical Chemistry. A
|March 15, 2012
Summary
This study investigated isopropylbenzenium ion complexes. Researchers found transient benzenium ion/propene complexes, but no stable benzene/isopropyl cation complexes, unlike tert-butyl cation complexes.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Organic Chemistry
Background:
- Ion-π electron complexes are crucial in chemical reactions.
- Understanding the stability of benzene-alkyl cation complexes is important.
Purpose of the Study:
- To investigate the potential for stable ion π-electron complexes in the isopropylbenzenium ion system.
- To determine if complexes of the type C(6)H(6)/C(3)H(7)(+) or C(6)H(7)(+)/C(3)H(6) exist.
Main Methods:
- Theoretical investigation using B3LYP for structure determination.
- High-accuracy composite methods (G3 (G3B3) and CBS (CBS-QB3)) for energy calculations.
- Potential Energy Surface (PES) analysis.
Main Results:
- Two minimum points on the PES corresponding to benzenium ion/propene complexes were identified, representing a single species due to rotation.
- A low barrier for forming the isopropylbenzenium ion from the complex suggests a short lifetime.
- No stable C(6)H(6)/C(3)H(7)(+) complex was found, but a quasi-stable species similar to C(6)H(6)/C(4)H(9)(+) was observed.
- An intense IR absorption line for C-H stretching was predicted for the complex.
Conclusions:
- Stable ion π-electron complexes of the benzene/isopropyl cation type are unlikely.
- The observed complexes are transient, with short lifetimes.
- A difference in stability compared to benzene/tert-butyl cation complexes was noted and a preliminary explanation provided.
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