25.1 Introducing Benzene

Question 1

Benzene chemical formula

Answer 1

C6H6

Question 2

Characteristics of benzene

Answer 2

Colourless, sweet smelling, highly flammable liquid

Classified as a carcinogen

Question 3

Where is benzene naturally found?

Answer 3

In crude oil, component of petrol

Question 4

Structure of benzene molecule

Answer 4

Hexagonal ring of 6 carbon atoms

Each carbon joined to 2 other carbon atoms and 1 hydrogen atom

Question 5

How is benzene classified?

Answer 5

As an aromatic hydrocarbon or arene

Question 6

Kekulé Model

Answer 6

Hexagonal ring of 6 Carbon atoms

Joined by alternate single and double bonds

Question 7

Evidence to disprove Kekulé’s Model

Answer 7

Lack of reactivity of benzene
Length of carbon carbon bonds in benzene
Hydrogenation enthalpies

Question 8

Lack of reactivity of benzene

Answer 8

If benzene had C=C bonds, it should decolourise bromine in an electrophilic addition reaction
However:
Benzene doesn’t undergo electrophilic addition reactions
Benzene doesn’t decolourise bromine at room temperature and pressure

Question 9

Length of Carbon-Carbon bonds in benzene

Answer 9

Using X ray diffraction, bond lengths in a molecule can be measured
It was found that all the bonds in benzene were 0.139nm in length
This is between the length of a single bond (0.153nm) and a double bond (0.134nm)