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[1] [2] In 1984, Glidewell and Lloyd provided an extension of Clar's rule to polycyclic aromatic hydrocarbons containing rings of any size. [3] More recently, Clar's rule was further extended to diradicaloids in their singlet state. [4] Two representations of the same resonance structure of anthracene.
According to Clar's rule, [20] the resonance structure of a PAH that has the largest number of disjoint aromatic pi sextets—i.e. benzene-like moieties—is the most important for the characterization of the properties of that PAH. [21] Benzene-substructure resonance analysis for Clar's rule
Erich Clar (23 August 1902 – 27 March 1987) was an Austrian organic chemist, born in Hřensko, who studied polycyclic aromatic hydrocarbon chemistry. He is considered as the father of that field. [ 1 ]
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Two different resonance forms of benzene (top) combine to produce an average structure (bottom). In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected by the stabilization of conjugation alone.
For the second generation reaction starting with the diazoketone, the reaction is performed by irradiation of a 0.7 M solution of the ketone with 1.0-1.2 equivalents of acetylene. A low-pressure mercury-vapor lamp at 254 nm in a photochemical reactor is used for 5–8 hours until all the diazoketone has been consumed as determined by TLC analysis.
The Buchner ring expansion is a two-step organic C-C bond forming reaction used to access 7-membered rings.The first step involves formation of a carbene from ethyl diazoacetate, which cyclopropanates an aromatic ring.
The lone pair of electrons on the anion then moves to the neighboring atom, thus expelling the leaving group and forming a double or triple bond. [1] The name of the mechanism - E1cB - stands for Elimination Unimolecular conjugate Base. Elimination refers to the fact that the mechanism is an elimination reaction and will lose two substituents.