Benzene & Kekule

From WikidChem

Faraday first isolated benzene, which he thought was C2H, and Liebig named it "benzol" It was then discovered that benzol also formed an acid, phenol (C6H5OH) Thus we call C6H5 phenyl from the Greek "phaenein" meaning to bring light because Faraday isolated benzene from illuminating gas.

Kekule listed reasons that he thought benzene was hexagonal, but they really did not provide any evidence other than that benzene had an almost radical characteristic (aromatics do not decompose past six carbons)

In his next paper, Kekule changed his notation and drew hypothetical hexagonal and triangular structures for benzene. In the hexagonal drawing, a halogen could substitute at each of the equivalent corners. This gives one monosubstituted isomer, three disubstituted isomers, three trisubstituted isomers, three tetrasubsituted isomers, one pentasubstituted isomer, and one hexasubstituted isomer. In the triangular drawing, a halogen could substitute at a corner or in the center of the line. This makes possible two monosubstituted isomers, four disubstituted isomers, and six trisubstituted isomers. thus counting isomers experimentally could distinguish between these two structures for benzene.