Benzene

Question 1

Formula of benzene

Answer 1

C6H6

Question 2

Structure of benzene info.

Answer 2

Delocalised pi orbitals, etc.

Question 3

Nitration of benzene mechanism

Answer 3

Reagents:

• Concentrated nitric acid
• Concentrated sulphuric acid
• Heat to 50 Degrees Celsius

Formation of NO2+ ions:

• H2SO4 + HNO3 —>(Reversible) [H2NO3]+ + H2SO4-
• [H2NO3]+ —>(Reversible) H20 + NO2+(nitronium ion)

Electrophilic substitution:

• NO2 acts as an electrophile in electrophilic substitution
• Benzene pi bond(ring) attacks the electrophile(positive ion)
• etc.

Overall:

-Benzene + Nitric acid(HNO3) —> Nitro benzene + water

Question 4

Method to purify a solid compound

Answer 4

Recrystallisation

Question 5

How to test for purity of a substance

Answer 5

• Chromatography
• If pure, only one substance separates on filter papers
• if impure, more than one substance will separate out

Melting Points:

• If substance is pure, it will all melt at one fixed temperature
• If substance is impure, it will all melt over a range of temperatures

Question 6

Mechanisms of recrystallisation

Answer 6

H

Question 7

Recrystallisation 6 mark question -

Answer 7

H

Question 8

Why do we purify products of organic synthesis?

Answer 8

-To increase atom economy
-To remove harmful substances from your organic molecule - e.g. makes medicines safer, less harmful
E.g. removal of sulphuric acid from 3-nitromethylbenzene

Question 9

Thin layer chromatography mechanism

Answer 9

H

Question 10

Stationary phase def

Answer 10

H

Question 11

Mobile phase def

Answer 11

H

Question 12

Rf value def

Answer 12

H

Question 13

When does benzene becomes named as a phenol?

Answer 13

• When another functional group is attached, e.g. OH

- when a carbon chain of 8 carbons or more is attached