25.2 Electrophillic substitution reactions of benzene

Question 1

What type of reactions does benzene undergo?

Answer 1

Substitution reactions

Question 2

What does benzene typically react with?

Answer 2

Electrophiles by electrophilic substitution

Question 3

What happens during electrophilic substitution reactions of benzene?

Answer 3

A hydrogen atom on the benzene ring is replaced by another atom or group of atoms

Question 4

What is the general equation representing electrophilic substitution in benzene?

Answer 4

Question 5

What is formed from the reaction of benzene with nitric acid?

Answer 5

Nitrobenzene, water

Question 6

What are the reagents and conditions for the nitration of benzene?

Answer 6

concentrated sulfuric acid (H2SO4), heated at 50°C

Question 7

What is the equation for the nitration of benzene?

Answer 7

Question 8

What happens if the temperature rises above 50°C in the nitration of benzene?

Answer 8

Further substitution reactions occur, leading to production of dinitrobenzene

Question 9

What is the equation showing further substitution in the nitration of benzene?

Answer 9

Question 10

What is nitrobenzene useful for?

Answer 10

Important starting material in preparation of dyes, pharmaceuticals and pesticides. Starting material in preparation of paracetamol

Question 11

What is the name of the mechanism for nitration of benzene?

Answer 11

Electrophilic substitution

Question 12

What is the electrophile used for nitration of benzene?

Answer 12

Nitronium ion NO2+

Question 13

How is a nitronium ion produced?

Answer 13

Reaction of nitric acid with concentrated H2SO4

Question 14

Draw the mechanism for the nitration of benzene

Answer 14

Question 15

When do halogens react with benzene?

Answer 15

When a halogen carrier is present

Question 16

What are common halogen carriers?

Answer 16

AlCl3, FeCl3, AlBr3, FeBr3

Question 17

How are halogen carriers generated?

Answer 17

In-situ (in a reaction vessel) from the metal and the halogen

Question 18

What is the name of the mechanism for the bromination of benzene?

Answer 18

Electrophilic substitution

Question 19

What are the reagents and conditions for the bromination of benzene?

Answer 19

Br2 halogen carrier (eg. FeBr3, AlBr3), RTP

Question 20

What are the reagents and conditions for the chlorination of benzene?

Answer 20

Cl2, halogen carrier (eg. FeCl3, AlCl3), RTP

Question 21

What is the equation for the bromination of benzene?

Answer 21

Question 22

Draw the mechanism for the bromination of benzene

Answer 22

Question 23

What happens in stage 2 of bromination of benzene?

Answer 23

Bromonium ion accepts a pair of electrons from the benzene ring to form a dative covalent bond

Question 24

What is the electrophile for bromination of benzene

Answer 24

Br+

Question 25

Why does benzene not react with non-polar bromine molecule?

Answer 25

Benzene is too stable

Question 26

What is the equation for the chlorination of benzene?

Answer 26

Question 27

Give an example of a halogen carried used for chlorination of benzene

Answer 27

FeCl3, AgCl3

Question 28

What is formed from the chlorination of benzene?

Answer 28

chlorobenzene, HCl

Question 29

What is formed from the bromination of benzene?

Answer 29

Bromobenzene, HBr

Question 30

What is the alkylation of benzene?

Answer 30

The substitution of a hydrogen atom in the benzene ring by an alkyl group

Question 31

What are the regents and conditions required for the alkylation of benzene (Friedel-Crafts alkylation)?

Answer 31

Haloalkane, in presence of AlCl3

Question 32

What is the purpose of AlCl3 in alkylation of benzene (Friedel-Crafts alkylation)?

Answer 32

Acts as a halogen carried catalyst generating the electrophile

Question 33

What does Friedel-Crafts alkylation do?

Answer 33

Increases the number of carbon atoms in a compound by forming carbon-carbon bonds

Question 34

What is the equation for the reaction of benzene with chloroethane?

Answer 34

Question 35

What is formed when benzene reacts with an acyl chloride?

Answer 35

Ketone, HCl

Question 36

What is the name of the mechanism for Acylation of benzene?

Answer 36

Electrophilic substitution

Question 37

What is the equation for the reaction of benzene with ethanoyl chloride?

Answer 37

Question 38

What are the regents and conditions required for the acylation of benzene?

Answer 38

Acyl chloride, AlCl3

Question 39

What is the mechanism for the reaction between cyclohexene and bromine?

Answer 39

Question 40

What is the mechanism for the reaction of alkenes with bromine?

Answer 40

Electrophillic addition

Question 41

What is the mechanism for the reaction of benzene with bromine?

Answer 41

Electrophilic substitution

Question 42

What is the equation for the reaction of cyclohexene with bromine?

Answer 42

Question 43

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

Answer 43

-Alkenes decolourise bromine by an electrophilic addition reaction, bromine adds across the double bond -Benzene does not react with bromine unless a halogen carrier catalyst is present, this is electrophilic substitution

Question 44

Why is the reactivity of benzene low?

Answer 44

-Due to the delocalised 𝛑-electrons spread above and beyond the plane of carbon atoms. The electron density around two C atoms is less than a C=C in alkene -When a non-polar molecule (eg.bromine) approaches benzene there is insufficient 𝛑-electron density to polarise the bromine molecule, preventing any reaction taking place

Question 45

Why is the reactivity of alkenes high for reaction with Br2?

Answer 45

-The 𝛑-bond in alkene contains localised electrons above and below the plane of the two carbon atoms, this produces an area of high electron density -The localised electrons in the 𝛑-bond induce a dipole in the non-polar bromine molecule making a one bromine slightly positive and another slightly negative -The slightly positive bromine atom enables bromine to act as an electrophile