Colour Design

Question 1

What is the difference between the reactions of alkenes and benzene?

Answer 1

Alkenes tend to undergo electrophilic addition reactions where as benzene tend to undergo substitution.

Question 2

Why do benzene undergo substitution reactions?

Answer 2

Because of the stable ring structure formed by delocalised electrons. It can maintain the delocalisation by replacing a hydrogen which aren’t involved with the delocalised electrons

Question 3

What is an electrophile?

Answer 3

Electron deficient species that are attracted to an electron rich centre, reacting by accepting an electron pair in order to form a nucleophile.

Question 4

What are some examples of electrophiles?

Answer 4

Hydronium ion, boron trifluoride, aluminium chloride and halogen molecules fluorine, chlorine, bromine and iodine

Question 5

What is bromination?

Answer 5

An example of an electrophilic aromatic substitution reaction where the electrophile forms a sigma bond to the benzene ring before a proton is removed to form a substituted benzene ring

Question 6

What is formed in bromination?

Answer 6

A benzene ring called bromobenzene

Question 7

What are the conditions of bromination?

Answer 7

A catalyst of FeBr3 is needed to make the Br2 more electrophilic by polarising it

Question 8

What is the role of the iron catalys?

Answer 8

To make the Br2 molecule more electrophilic

Question 9

How is the iron catalyst in bromination different to traditional transition metal catalysts?

Answer 9

It gets permanently changed during the reaction to form iron (III) bromide.

Question 10

What is the equation for the reaction between bromine and the iron catalyst?

Answer 10

2Fe + 3Br2 –> 2FeBr3
H+ + FeBr4- –> HBr +FeBr3

Question 11

What is chlorination?

Answer 11

It is an electrophilic substitution reaction between chlorine and benzene

Question 12

What is the product of chlorination?

Answer 12

A mixture of mono and dichlorobenzenes

Question 13

What are the conditions for chlorination?

Answer 13

Room temp, in the presence of an aluminium catalyst (normally) and under anhydrous conditions

Question 14

Why is chlorination done at room temp?

Answer 14

Due to the combination of reactive chlorine and powerful halogen carrier aluminium chloride

Question 15

Why must chlorination occur under anhydrous conditions?

Answer 15

Because aluminium chloride reacts violently with water

Question 16

What is the role of the aluminium catalyst in chlorination?

Answer 16

It acts as a Lewis Acid catalyst by enhancing the electrophilicity of chlorine, generating a more reactive electrophile.

Question 17

What is the equation for the formation of the electrophile?

Answer 17

Cl2 + AlCl3 –> AlCl4- + Cl+

Question 18

Why are halogenated benzene derivatives so important?

Answer 18

They have been found to be important intermediates in synthetic routes and the carbon atom attached to the halogen can attack other carbon atoms, allowing C-C bonds to form

Question 19

What is alkylation?

Answer 19

Alkylation involves the substitution of an alkyl group onto a benzene ring by replacing a hydrogen with a group like methyl or ethyl ect.

Question 20

What are the conditions for alkylation?

Answer 20

Benzene is reacted with chloroethane and anhydrous aluminium chloride under reflux

Question 21

What is the role of AlCl3 in alkylation?

Answer 21

The AlCl3 acts as a catalyst and a reactant in the formation of the electrophile.

Question 22

What is the equation for the formation of the electrophile in alkylation?

Answer 22

CH3CH2Cl + AlCl3 –> CH3CH2+ + AlCl4-

Question 23

What is an acyl group?

Answer 23

an alkyl group attached to a C=O bond

Question 24

What are the conditions for acylation?

Answer 24

Reacting with an acyl chloride (or acid anhydride) and aluminium chloride under anhydrous conditions

Question 25

What is the equation for the formation of the electrophile in acylation?

Answer 25

CH3COCl +AlCl3 --> CH3CO+ + AlCl4-

Question 26

Why are the Friedel-Crafts reactions so important?

Answer 26

They are able to transform simple aromatic compounds into more complex ones which is useful in the synthesis of medicines, dyes, polymers and other organic materials

Question 27

What do arenes and aromatic compounds include?

Answer 27

A benzene ring

Question 28

How does the Kekule model of benzene describe the length of the bonds?

Answer 28

There should be 3 bonds the length of a C-C bond and 3 bonds the length of a C=C bond

Question 29

How did they discover the true length of the bonds within benzene?

Answer 29

Through x-rays diffraction studies, they discovered the C-C bonds are the same length

Question 30

How does the delocalised model of benzene explain benzene's properties?

Answer 30

The carbons are arranged within a ring, but there are no alternating single, double bonds and instead each carbon donates and electron form its p-orbital and the p-orbitals combine to form a ring of delocalised electrons

Question 32

What kind of reaction does benzene undergo?

Answer 32

Substitution reaction- a hydrogen gets swapped with something else, keeping the stability of the delocalised electrons

Question 33

Why is the ring within benzene stable?

Answer 33

The electrons have more room to spread out than if they were in localised double bonds meaning they can get further away from one another, spreading out the negative charge to become more stable.

Question 34

What would you expect the enthalpy change of benzene to be if the Kekule model was correct?

Answer 34

You would expect it to have an enthalpy change 3x that of a single C=C bond. However, it is only -208kJ mol-1

Question 35

What type of reaction do arenes undergo?

Answer 35

Electrophilic Substitution

Question 36

How do you make nitrobenzene?

Answer 36

Warm benzene with conc. nitric and sulfuric acid. 1.Sulfuric acid as a catalyst helps to make NO2+ which is an electrophile. 2. In order to only add one NO2 group, you need to keep the temperature between 55c