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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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The excited state antiaromatic benzene ring: a molecular Mr Hyde?
Raffaello Papadakis1, Henrik Ottosson
1Department of Chemistry - BMC, Uppsala University, Box 576, 751 23 Uppsala, Sweden. Henrik.Ottosson@kemi.uu.se.
Chemical Society Reviews
|May 12, 2015
Summary
Benzene exhibits antiaromatic character in its excited triplet state, a phenomenon confirmed by quantum chemical calculations. This "Mr. Hyde" aspect of benzene influences its photochemical reactivity, offering new insights into molecular behavior.
Area of Science:
- Theoretical and computational chemistry
- Photochemistry
- Organic chemistry
Background:
- Baird's rule, established over four decades ago, predicts antiaromaticity in annulenes' triplet states.
- This rule contrasts with Hückel's rule for ground-state aromaticity.
- High-level quantum chemical calculations have consistently confirmed Baird's rule for benzene.
Purpose of the Study:
- To review theoretical and computational studies confirming Baird's rule for benzene's excited states.
- To explore the implications of benzene's excited-state antiaromaticity on its photochemical reactivity.
- To highlight the often-overlooked "Mr. Hyde" character of benzene's excited states.
Main Methods:
- Review of existing theoretical and computational studies.
- Analysis of photochemical reactions in benzene derivatives.
- Application of perturbation molecular orbital (PMO) theory concepts.
Main Results:
- Baird's rule is confirmed for benzene's lowest triplet (T1) and singlet (S1) excited states.
- Excited-state antiaromaticity significantly influences the photochemical reactivity of benzene derivatives.
- Benzene displays a dual "Dr. Jekyll and Mr. Hyde" character due to its ground-state aromaticity and excited-state antiaromaticity.
Conclusions:
- Benzene's excited-state antiaromaticity is a crucial factor in its photochemistry.
- Recognizing this dual character can provide novel perspectives in various chemical applications.
- Further research into excited-state antiaromaticity can unlock new avenues in molecular design and reactivity.
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