Structure of benzene Flashcards
What is the 3 pieces of evidence against Kekules model?
Bond lengths, enthalpy of hydrogenation data and types of reactions of benzene
What is the bond lengths evidence?
All the bonds in benzene are of equal length, whereas single and double bonds have different lengths
What is Kekule’s model?
A 6C ring with alternating single and double bonds
How does bond length evidence disprove Kekule’s model?
His model had alternate long and short bonds, and benzene doesn’t have bond lengths which match either single or double bonds
What s the enthalpy of hydrogenation data evidence?
Benzene has a higher enthalpy of hydrogenation data that cyclohexane
How does the enthalpy of hydrogenation data disprove Kekule’s model?
Benzene is more stable that expected for his structure
What is the types of reaction evidence?
Benzene mainly undergoes substitution reactions
How does the types of reactions evidence go against Kekule’s model?
His modern would be expected to undergo addition reactions, but if it did, it’d lose the delocalised pi bond and the extra stability
What is the bonding in benzene?
The p orbitals overlap laterally on both sides, and a pi system of 2 rings of delocalised electrons form above and below the carbon ring
Why is the bonding in benzene known as the delocalised model?
The 6 pi electron are shared by all 6 carbon atoms
