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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
The substituent effect on benzene dications
Marcin Palusiak1, Małgorzata Domagała, Justyna Dominikowska
1Department of Theoretical and Structural Chemistry, University of Łódź, Pomorska 163/165, 90-236 Łódź, Poland. marcinp@uni.lodz.pl.
Benzene dicationic forms are more sensitive to substituent effects than neutral benzene. Aromaticity indices require careful use for charged benzene analogues, especially differentiating singlet and triplet states.
Area of Science:
- Computational Chemistry
- Organic Chemistry
- Quantum Chemistry
Background:
- Neutral benzene and its 4n+2 π-electron analogues exhibit resistance to substituent effects due to delocalized character.
- The 4n π-electron dicationic form of benzene is hypothesized to be more susceptible to substituent effects.
Purpose of the Study:
- To investigate the impact of single and double substitution on benzene dication's susceptibility to substituent effects.
- To compare the behavior of dicationic benzene with neutral benzene under substitution.
- To analyze differences between singlet and triplet states of dicationic benzene.
Main Methods:
- Computational assessment using various aromaticity indices.
- Evaluation using the Substituent Effect Stabilization Energy (SESE) parameter.
- Analysis of para- and meta-substitution effects on dicationic benzene.
Main Results:
- Dicationic benzene is significantly more sensitive to substitution than neutral benzene.
- Dicationic benzene acts as a strong electron-withdrawing center, interacting cooperatively with electron-donating and anticooperatively with electron-withdrawing substituents.
- Triplet state dicationic benzene is more delocalized and less sensitive to substituents than the singlet state.
- Disubstituted dicationic benzene shows distinct behavior from neutral benzene, with different substitution mechanisms.
- Double ionization reduces aromaticity in singlet dicationic benzene but conserves it in the triplet dicationic form.
Conclusions:
- Aromaticity indices can be misleading for charged benzene analogues and should be used cautiously.
- The electronic nature and spin state of dicationic benzene significantly influence its response to substituents.
- Substitution patterns in dicationic benzene differ mechanistically from those in neutral benzene.
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