The Kekule Structure For Benzene printable pdf download

The Kekule Structure For Benzene

C h e m g u i d e – q u e s t i o n s

THE KEKULÉ STRUCTURE FOR BENZENE

1. a) Benzene has the molecular formula C

. Draw the Kekulé structure for this showing all the

atoms.

b) Now draw the skeletal structure showing the way the Kekulé structure is normally drawn.

2. Ethene and benzene react with bromine in quite different ways. With ethene, bromine reacts with

an addition reaction:

=CH

+ Br

Br-CH

With benzene, you get a substitution reaction in which one of the hydrogen atoms is replaced by a

bromine:

+ Br

Br + HBr

Explain why this throws doubt on the accuracy of the Kekulé structure.

3. The carbon atoms in a benzene molecule are arranged in a perfect hexagon. Explain why this is

inconsistent with the Kekulé structure.

4. The following diagram shows the amount of energy released when a number of ring compounds

react with hydrogen to form cyclohexane.

The dotted lines represent values for the amount of heat released estimated from the cyclohexene

value. Solid lines represent the actual amounts of heat released from the real compounds.

a) Why is it reasonable to think that the value for the middle compound would be twice that of

cyclohexene?

b) What does the large discrepancy between the real and estimated values for benzene show?

The Kekule Structure For Benzene