ELECTROPHILIC SUBSTITUTION

Question 1

outline the mechanism of electrophile substituation

Answer 1

>the electron dense ring attracts electrophiles
>electrophile accepts a pair of pi electrons from the delocalised ring to form a new covalent bond.
>an intermediate us formed that contains both the electrophile and the hydrogen atom that is being substituted
>the delocalise pi electron cloud has been disrupted and the intermediate is less stable than benzene
>the unstable intermediate rapidly loses the hydrogen as an ion
>the delocalised ring of electrons is reformed and stability is restored

Question 2

Write an aquation for the formation of nitronium ion

Question 3

Outline the mechanism for nitration of benzene

Answer 3

1. Delocalised benzene ring is an area if high electron density and its prone to elctrophile attack
2. the electrophile NO2+ accepts a pair of π electrons from the delocalised ring to form a new covalent bond
3. An unstable intemediate is formed.The delocalised π elctron cloud has been disrupted and the intemediate is less stable than benzene
4. The unstable intermediate rapidly loses hydrogen as an ion as the C-H covalent bond is broken
5. The delocalised ring of pi electrons is reformed and stability is restored​

Question 4

Why does sulfuric acid acts as a catalyst in the mechanism

Answer 4

• Because it is regenerated at the end of the mechanism
• H+ + HSO4- >H2SO4

Question 5

under normal conditions what is needed for Benzene to react with halogens

Answer 5

• halogen carrier

Question 6

outline the mechanism of chlorine electrophilic substititution

Answer 6

1. AlCl3 helps polarises Cl2 to Cl+
2. As a result Cl+ is a stronger electrophile therefore accepts a pair of pi electrons in the delocalised ring to form a new covalent bond
3. An unstable intermediate is formed,which rapidly loses hydrogen as an ion when C-H bonds are broken
4. aluminium chloride is regenerated in the second stage by combining with the hydrogen ion

stage 1

Stage 2