|MadSci Network: Chemistry|
Hello Haresh, Benzene was first isolated from illuminating gas in 1825 by Michael Faraday. He determined its emperical formula to be CxHx. That means he figured out it had the same number of carbons as hydrogens. A German by the name of Mitscherlich found, in 1834, that pyrrolysis of lime of benzoic acid produced benzene and he correctly deduced its formula to be C6H6. During the later part of the nineteenth century structures were proposed which accounted for the molecular formula AND the unreactivity of benzene towards reagents which normally react with double bonds. Kekule was the first to propose, in 1865, the correct structure as a symmetric ring of six carbons with one hydrogen attached to each carbon. He predicted that benzene was an equilibrium mixture of two cyclohexatriene molecules. An interesting wrong structure was proposed by Ladenberg in 1879. It was later dubbed "prismane" and consists of two rings, of three carbons each, bonded to eachother through the three carbons of each ring. Each carbon then has only one hydrogen bonded to it and the molecule satisfies both the requirement for symmetry and the molecular formula. Of course it is NOT benzene but it was eventually synthesized by researchers at Columbia in 1973 and shown to isomerize to benzene upon heating to 90 degrees celcius. With the advent of quantum mechanics in the 20th century a more sophisticated understanding of benzene (and other aromatic systems) arose and it is now commonly accepted that benzene is NOT an equilibrating mixture of cyclohexatrienes but in fact one compound with all carbon-carbon bond lengths identical. Hope this info helps! Jeremy Starr.
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