Benzene

Question 1

What is the formula of Benzene

Answer 1

C6H6

Question 2

Why is Benzene more stable than cyclohexa-1,3,5-triene

Answer 2

Because contains delocalised electrons

Question 3

Draw the structure of Benzene and Cyclohexa-1,3,5- triene

Question 4

State the evidence for delocalised bonding in Benzene

Answer 4

• The planar structure
• The intermediate bond length
• The stability

Question 5

Intermediate bond length

Answer 5

if benzene had an alternating double bond - single bond structure it would have 2 diff bond lengths. Double bonds are shorter than single bonds. All bonds within benzene are the same length an intermediate between double and single. So Benzene does not have alternating bonds

Question 6

Enthalpies of hydrogenation evidence for Benzene stability

Answer 6

The enthalpy of hydrogenation of cyclohexene is - 120kJmol^-1
So the enthalpy change for the hypothetical cyclohexa-1,3,5-triene is -360.
The actual enthalpy change of hydrogenation for benzene is -208 so benzene is more stable than an alternating double bond - single bond structure

Question 7

What type of mechanism does Benzene undergo

Answer 7

Electrophilic substitution rather than addition because the aromatic ring is very stable as a large amount of energy is needed to break the ring system so the ring structure will remain intact

Question 8

What type of mechanism does Benzene undergo

Answer 8

Electrophilic substitution rather than addition because the aromatic ring is very stable as a large amount of energy is needed to break the ring system so the ring structure will remain intact
.

Question 9

What is Free Crafts Acylation

Answer 9

add acyl chlorides to benzene rings with AlCl3 as a catalyst = AlCL4- ions and RCO+.
RCO+ is attacked by the electrons of the benzene ring.
Hydrogen is released from the ring to form an aromatic ketone and HCl and reform the AlCl3 catalyst.