PROBLEMS WITH KEKULES STRUCTURE (5POINTS)

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  • Created by: Bela
  • Created on: 10-03-12 15:01
  • 1) the absence of 1,2 disubstituted isomers. E.g 1,2 dichlorobenzene: should be 2 isomers, one with 2 chlorine atoms attached to 2 carbons that are joined by a double bond; and the other, 2 chlorine atoms attached to 2 carbons joined by a single bond. There was never been 2 separate isomers distinguished. 
  • 2)Bond lengths: in a aliphatic compound, the c=c bond is shorter than the c-c bond. From kekules structure- expect- three bonds=same length, with a length the same as a c-c bond in an alkane, and the other three bonds=different length, with a length the same as a c=c bond in an alkene. However by x-ray diffraction- shows all carbon atoms are arranged at the edges of a regular hexagon. Hence all bonds are same length. Also when looking at an electron density map- significant electron density above and below the plane of 6 carbon atoms
  • 3)Resistance to reaction of benzene- would expect kekules structure for benzene to react in a have a similar chemical behaviour to a reactive alkene and so undergo electrophillic addition reactions with bromine and hydrogen bromide. However benzene is characteristic of substitution reactions rather than addition= shows it's less…

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