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The model for benzene consists of two resonance forms, which corresponds to the double and single bonds superimposing to give rise to six one-and-a-half bonds. Benzene is a more stable molecule than would be expected without accounting for charge delocalization.
As benzene is ubiquitous in gasoline and hydrocarbon fuels that are in use everywhere, human exposure to benzene is a global health problem. Benzene targets the liver, kidney, lung, heart and brain and can cause DNA strand breaks and chromosomal damage, hence is teratogenic and mutagenic. Benzene causes cancer in animals including humans.
In other words, a polycyclic aromatic hydrocarbon with a given number of π-sextets is more stable than its isomers with fewer π-sextets. [ 1 ] [ 2 ] In 1984, Glidewell and Lloyd provided an extension of Clar's rule to polycyclic aromatic hydrocarbons containing rings of any size. [ 3 ]
The trans isomer is more stable by approximately 50 kJ/mol, and the barrier to isomerization in the ground state is approximately 100 kJ/mol. Azobenzene photoisomerization. The trans form (left) can be converted to the cis form (right) using a UV wavelength of 300–400 nm. Visible illumination at >400 nm converts the molecule back to the trans ...
Contributing structures of the carbonate ion. In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or forms, [1] also variously known as resonance structures or canonical structures) into a resonance hybrid (or hybrid structure) in valence bond theory.
In the following keto-enol tautomerization, the product enol is more stable than the original ketone even though the ketone contains an aromatic benzene moiety (blue). However, there is also an antiaromatic lactone moiety (green). The relief of antiaromatic destabilization provides a driving force that outweighs even the loss of an aromatic ...
In chemistry, chemical stability is the thermodynamic stability of a chemical system, in particular a chemical compound or a polymer. [1] Colloquially, it may instead refer to kinetic persistence, the shelf-life of a metastable substance or system; that is, the timescale over which it begins to degrade.
Meanwhile, the domino products 6 are more thermodynamically stable than 5 (ΔG ‡ ≈ 4.2-4.7 kcal/mol) and this fact may cause isomerization of 5 into 6 at elevated temperature. Indeed, the calculated activation barriers for the 5 → 6 isomerization via the retro-Diels–Alder reaction of 5 followed by the intramolecular [4+2]-cycloaddition ...