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Published on: April 19, 2019
Protonated tert-pentyl dication (C5H122+, isopentane dication).
George A Olah1, G K Surya Prakash, Golam Rasul
1Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, University Park, Los Angeles, CA 90089-1661, USA. olah@usc.edu
Dalton Transactions (Cambridge, England : 2003)
|January 11, 2008
Summary
Computational chemistry reveals two stable structures for the tert-pentyl cation, with similar energies. The protonated dication
Area of Science:
- Computational Chemistry
- Physical Organic Chemistry
- Quantum Chemistry
Background:
- Carbocation structures and stability are fundamental in organic chemistry.
- Hyperconjugation plays a significant role in stabilizing carbocations.
- Understanding dicationic species provides insights into extreme chemical environments.
Purpose of the Study:
- To determine the stable structures of the tert-pentyl cation (C(5)H(11)(+)) and its protonated dication (C(5)H(12)(2+)).
- To investigate the energetic relationships and interconversion barriers between different cationic forms.
- To analyze the electronic effects of an additional charge on the dication's properties.
Main Methods:
- Ab initio electronic structure calculations were performed.
- The MP2/cc-pVTZ level of theory was employed for high accuracy.
- Potential energy surfaces were explored to identify minima and transition states.
Main Results:
- Two hyperconjugatively stabilized structures (C-C and C-H) were identified as minima for the tert-pentyl cation.
- These two structures exhibit comparable stability, with a small energy difference of 0.5 kcal mol(-1).
- A low kinetic barrier of 1.5 kcal mol(-1) facilitates interconversion between the two cationic forms.
- The C-H protonated structure was found to be the global minimum for the protonated tert-pentyl dication.
Conclusions:
- Both C-C and C-H hyperconjugation are significant stabilizing factors for the tert-pentyl cation.
- The protonated tert-pentyl dication adopts a specific C-H protonated configuration as its most stable form.
- Calculated charges and NMR shifts highlight the impact of the additional charge in the dication.
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