MadSci Network: Chemistry

Re: What chemist deduced that benzene was a closed carbon hexagonal chain?

Area: Chemistry
Posted By: Jeremy Starr, Grad Student, Chemistry, California Institute of Technology
Date: Fri Jul 18 17:40:27 1997
Area of science: Chemistry
ID: 869106278.Ch
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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