Structure of benzene

Question 1

Why was kekules model of benzene proven wrong??

Answer 1

• Doesn’t rapidly decolourise bromine water like an alkene would (C=C) too stable to react
• All bonds were deemed the same length: kekule’s model contained 3 C-C and 3 C=C, that are different lengths.
• Enthalpy of hydrogenation less exothermic than expected (no C=C bonds) more energy needs to be put in

Question 2

What are the features of the current model of Benzene??

Answer 2

• 6 P orbitals that overlap above and below the carbon ring, creating de localised system
• Adjacent p orbitals share 6 delocalised electrons, forming pi bonds
• Sigma bonds betweens carbons and hydrogens.
• 120 degrees ( trigonal planar shape) around each carbon (one hydrogen and 2 carbons)

Question 3

What does a 3 mark labelled diagram of the benzene structure contain

Answer 3

Carbon ring, P orbitals overlapping above and below the carbon ring, forming Pi bonds