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It was introduced in 1972 by the Austrian organic chemist Erich Clar in his book The Aromatic Sextet. The rule states that given a polycyclic aromatic hydrocarbon , the resonance structure most important to characterize its properties is that with the largest number of aromatic π-sextets i.e. benzene-like moieties .
Prismane or 'Ladenburg benzene' is a polycyclic hydrocarbon with the formula C 6 H 6. It is an isomer of benzene , specifically a valence isomer . Prismane is far less stable than benzene.
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.
Some were originally proposed for benzene itself before the actual structure of benzene was known. Others were later synthesized in lab. Some have been observed to isomerize to benzene, whereas others tend to undergo other reactions instead, or isomerize by ways other than pericyclic reactions. Some known valence isomers of benzene
In organic chemistry, benzenoids are a class of organic compounds with at least one benzene ring. These compounds have increased stability due to resonance in the benzene rings. Most aromatic hydrocarbons are benzenoid. Notable counterexamples are cyclooctadecanonaene, azulene and trans-bicalicene. [1] [2]
*** Benzene is a carcinogen (cancer-causing agent). *** Very flammable. The pure material, and any solutions containing it, constitute a fire risk. Safe handling: Benzene should NOT be used at all unless no safer alternatives are available. If benzene must be used in an experiment, it should be handled at all stages in a fume cupboard.
The best-known example is benzene (C 6 H 6) with a conjugated system of six π electrons, which equals 4n + 2 for n = 1. The molecule undergoes substitution reactions which preserve the six π electron system rather than addition reactions which would destroy it. The stability of this π electron system is referred to as aromaticity. Still, in ...
In alkanes, optimum overlap of atomic orbitals is achieved at 109.5°. The most common cyclic compounds have five or six carbons in their ring. [6] Adolf von Baeyer received a Nobel Prize in 1905 for the discovery of the Baeyer strain theory, which was an explanation of the relative stabilities of cyclic molecules in 1885.