Arenes

Question 1

Properties of benzene

Answer 1

• colourless liquid at rtp
• non-polar
• C:H is 1:1
• toxic and found carcinogenic

Question 2

Structure of benzene

Answer 2

• flat, symmetrical molecule with shape of regular hexagon
• C-C bond angle is 120 degrees
• cloud of delocalise pie electrons lying above and below the ring
• resonance in benzene

Question 3

Chemical properties of benzene

Answer 3

• cloud of delocalised pie electron of the ring is a region of high electron density susceptible to attach by electrophiles
• undergo substitution reactions under suitable conditions to retain its resonance stabilised ring system

Question 4

Reactions of benzene

Answer 4

• Nitration
• Halogenation
• Freidel-Crafts alkylation

Question 5

Substitution of mono-substituted benzene derivatives
- how does prescence of G affects reactivity towards further electrophilic substitution

Answer 5

• G may release electrons into the benzene ring
• increases electron density of ring compared to unsubstituted benzene
• electrophiles more attracted towards the benzene ring
• rate of electrophilic substitution is faster
• G is an activating group

Question 6

Activating and 2- and/or 4- directing substituents

Answer 6

• they are electron donating groups
• increases electron density in the pie electron cloud of the ring and thus increases attraction of electrophiles
• increases rate of electrophilic substitution of benzene ring compared to unsubstituted benzene
• direct incoming electrophiles o 2nd and 4th positions

Question 7

Deactivating and 3-directing subtituents

Answer 7

• they are electron-withdrawing groups
• reduces electron density in the pie electron cloud of the ring and thus reduces attraction towards electrophiles
• decreases rate of electrophilic substitution of benzene ring compared to unsubstituted benzene
• direct electrophile to the 3rd position

Question 8

Deactivating and 2- and/or 4- directing substituents

Answer 8

• halogens deactivate the ring by electronic effect but direct further substitution to 2nd and 4th position due to its ability to stabilise the carbocation intermediate via resonance effect

Question 9

Reactions of methylbenzene
- ring
- side chain

Answer 9

• nitration
• halogenation
• alkylation
• free radical substitution
• oxidation