Aromatic Compounds

Question 1

Why do benzene molecules not undergo typical alkene reactions?

Answer 1

Resonance -> delocalisation of electrons around the ring increases stability

Question 2

Name a benzene ring with a methyl group attached

Answer 2

Toluene

Question 3

How do you name disubstituted benzene?

Answer 3

Ortho 1,2

Meta 1,3

Para 1,4

Question 4

What reactions do benzene rings undergo?

Answer 4

Electrophilic aromatic substitution

Question 5

What are the steps to electrophilic aromatic substitution?

Answer 5

Electrophilic attack -> a pair of electrons from the benzene ring are donated to the electrophile

This forms a number of resonance stabilised cation s with the cation on the ortho and para positions relative to the electrophile bonded carbon -> resonance hybrid

Elimination occurs as the electrons from the C-H bond are donated to the ring and the H leaves

Question 6

What is the reactivity of benzene ring?

Answer 6

Benzene is unreactive because it has many resonance stabilised cation intermediate forms

Question 7

What are electrophiles that can cause electrophilic aromatic substitution?

Answer 7

Halogen - Cl+, F+, Br+

Nitro group - NO2+

Ketone group - RCO+

Alkyl groups

Question 8

How do you form halogen electrophile?

Answer 8

Cl - Cl + FeCl3 -> Cl+ + FeCl4-

Heterolytic bond cleavage of the Cl2

Question 9

How do you form nitro group- electrophile?

Answer 9

HNO3 + H2SO4 -> NO2+ HSO4- + H2O

Question 10

What is friedel-crafts acylation?

Answer 10

Use of AlX3 to generate a ketone group (electrophile) to add on to benzene ring

Question 11

What is friedel-crafts alkylation?

Answer 11

Use of AlX3 to generate an alkyl group to add on to benzene ring

Question 12

What happens when you mix a primary alkyl halide and AlCl3?

Answer 12

The primary carbocation rearranges to form secondary -> positive inductive effect ie distribution of charge means secondary carbocation is more stable

Question 13

What are the reagents to go from benzene to nitrobenzene?

Answer 13

HNO3/H2SO4

Question 14

What are the reagents to go from benzene to alkylbenzene?

Answer 14

AlkylCl + AlCl3

Question 15

What are the reagents to go from benzene to halogen substituted benzene?

Answer 15

X2 + FeX

Question 16

What are the reagents to go from nitrobenzene to aniline?

Answer 16

Fe/H+

Then NaOH

Question 17

What are the reagents to go from aniline to diazonium ion?

Answer 17

Add HNO2

at 0 degrees celsius

Question 18

How do you form phenol from benzene ring?

Answer 18

Benzene

Add HNO3/H2SO4

Nitrobenzene

Add Fe/H+ then OH-

Aniline

Add HNO2 at 0C

Diazonium ion

Add H3O+

Phenol

Question 19

How do you form benzonitrile?

Answer 19

Benzene

Add HNO3/H2SO4

Nitrobenzene

Add Fe/H+ then OH-

Aniline

Add HNO2 at 0C

Diazonium ion

Add CuCN

Benzonitrile

Question 20

How do you go from nitrile to carboxylic acid?

Answer 20

Add acid or base

Question 21

What are the factor to consider when determining the position of the substituent groups of a disubstituted benzene?

Answer 21

Where does substitution occur initially -> ortho, meta, para

Will the reaction occur more or less readily than for the same electrophile with benzene -> is the first substituent group activating or deactivating

Question 22

How do you determine to what position the second substituent of a benzene ring will be added to?

Answer 22

Consider whether the group is activating or deactivating

Activating -> electron donating (species with lone pair for donation into the ring + alkyl groups for induction)
Deactivating -> electron withdrawing (sp2 carbons with polar bond)

If activating -> ortho, para more likely
If deactivating -> meta more likely

Consider the number of reasonable resonance contributors for carbocation intermediate -> postively charged species cant be together

More number = more stable = more likely to form