4. Electron Sharing and      Covalent Bonds  
     Double and Triple Bonds

A special kind of multiple bonding, which we will learn later is vital in energy-trapping molecules such as chlorophyll, is illustrated by benzene,C6H6 ;. As indicated on the right, the six carbon atoms in benzene are linked into a hexagon, with each carbon atom bonded to two other carbon atoms and one hydrogen atom. This leaves each of the six carbon atoms with one additional electron, and these six electrons are the raw materials for three more electron-pair bonds. One way of picturing these bonds would be an alternation of single bonds and double bonds around the hexagon, as shown in the right. This would imply an alternation of long and short C-C bonds around the ring, yet every physical measurement that we can carry out on benzene suggests that all of the C-C bonds are alike.

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