What are the Kekule structures

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benzene

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  • benzene
  • engl.: benzene
  • C.6H6
  • Benzene was discovered by M. Faraday in 1825 and described under the name "gasoline". The proposal to describe benzene as a six-membered ring-shaped compound with alternating single and double bonds goes back to A. Kekulé (1865) (Fig. 1). Today the Kekulé formula is regarded as a mesomeric limit form (Fig. 2) because all bonds in the benzene molecule are of the same length (1.390 Å) and are chemically similar. Another established form of formula notation is the hexagon proposed by R. Robinson with an inner circle (Fig. 3).
  • Benzene is an easily mobile, colorless, highly refractive liquid with an aromatic odor. It is highly flammable and burns with a bright, sooty flame. Benzene fumes are very toxic and carcinogenic, so it is replaced by toluene in the laboratory wherever possible.
  • Benzene mixes completely with methanol, ethanol, ethyl acetate, acetone and many other organic solvents. It only slightly dissolves in water (1.770 g L.-1 at 20), but forms an azeotrope with 8.83% water that boils at 69.25.
  • Benzene is a component of fuels and is used as a starting material for many syntheses. In 1998 the annual production of benzene was 28 million.