6.1.1 Phenols

Question 1

What is the reaction when more than one Br atom substitutes onto the benzene ring ?

Answer 1

Multisubstitution

Question 2

Nitration of phenol

• Reagents
• Conditions

Answer 2

• dilute HNO3(aq)

- room temperature, no catalyst needed

Question 3

Bromination of phenol

• Reagents
• Conditions
• observations

Answer 3

• Br2 (aq) solution
• room temperature, no catalyst needed
• few drops of Br2: orange to colourless
• with excess Br2: white precipitate

Question 4

Reactivity of phenol

Answer 4

• phenol has 2 functional groups
• the benzene ring which undergoes electrophilic substitution
• and the hydroxy OH which undergoes neutralisation reactions with alkalis, and redox reactions with reactive metals (Na,K,Li)

Question 5

How to distinguish between alcohols, phenols and carboxylic acids

Answer 5

• All 3 react with reactive metals in a redox reaction
• Alcohols are neutral and won’t react with alkalis or metal carbonates
• Phenols are wear acids (5-6) than carboxylic acids (2-4) and will react with alkalis but will not react with metal carbonates
• Carboxylic acids will react with metal carbonates and produce fizzing
  Equation: 2CH3COOH + NaCO3 -> 2CH3COONa + CO2 + H2O
  Ionic (always will be this): 2H+ + CO3 2- -> CO2 + H2O

Question 6

Why is phenol more reactive than benzene with electrophiles such as bromine water or nitric acid?

Answer 6

• The lone pair of e- in a p-orbital on the oxygen atom of the OH group is delocalised into the pi bond of the benzene ring (activation of the benzene ring)
• which increases the electron density of the benzene ring
• which in turn attracts electrophiles more strongly and induces bigger positive dipoles on the electrophile
• Other groups attracted to the benzene ring such as NH2 or Cl also activate the benzene ring and make it more reactive by delocalising an e- pair into the pi bond of the benzene ring

Question 7

What happens during further substitution?

Answer 7

If a benzene ring already has one group attached, the group will direct another electrophile to attach at either the 2 & 4 C position, or at the 3 C position

Question 8

What are 2,4 directing groups?

Answer 8

• They direct electrophiles to 2 and 4 positions because they activate the benzene ring (push in pi e-)
• Carbon positions 2 and 4 end up with a higher pi electron density which attracts electrophiles more strongly