AC5: Phenols

Question 1

What is a phenol

Answer 1

A hydroxyl group attached to a benzene ring

Question 2

Describe the acidity of phenol

Answer 2

Phenol is a weak acid

Question 3

Describe and explain why phenol can more readily ionise than alcohols

Answer 3

The phenoxide ion formed when phenol releases a proton, is stable due to the charge on the oxygen being able to delocalise into the π - electron system, so, phenol can more readily ionise and donate a proton (to act as an acid) compared to alcohols which are neutral

Question 4

Do phenols more or less readily ionise (donate a proton) than alcohols

Answer 4

Phenols more readily ionise than alcohols

Question 5

What type of bases does phenol react with

Answer 5

only with strong bases - Na OH
not with weak bases - CO3(2-), HCO3 (2-)

Question 6

Describe and explain the solubility of phenol

Answer 6

Phenol is partially soluble in cold water, as the hydroxyl group is able to form H-bonding with water, but there is a large non-polar group (benzene ring) that does not from strong attractions to water, hence phenol is only partially soluble

Question 7

Compare the solubility of phenol with a salt of phenol (phenoxide ion + Sodium ion)

Answer 7

The salt is more soluble than phenol as it is ionic and can form ion-dipole bonds with water that are stronger than H-bonds

Question 8

Compare and explain the reactivity of phenols with benzene

Answer 8

phenol is more reactive than benzene because the lone pair of electrons in the p-orbital of the oxygen of the hydroxyl group delocalises into the π - electron system, increasing the electron density of the ring and making it more attractive to electrophiles

Question 9

Describe what happens when phenol goes through a halogenation reaction with bromine

Answer 9

bromine decolourises and a white precipitate forms, white fumes of HBr may be seen

Question 10

Is a catalyst required for the halogenation of Phenol, and compare this to with benzene

Answer 10

NO whereas you need a halogen carrier AlBr3 for benzene

Question 11

Is a catalyst required for the nitration of Phenol, and compare this to with benzene

Answer 11

NO whereas you need conc HNO3, conc H2SO4 and 50-60 ºC for benzene

Question 12

What is an electron donating group on an aromatic ring and explain how it works

Answer 12

Substituent groups that “activate” the aromatic ring e.g. hydroxyl group or amine group
The lone pair(s) on the O of hydroxyl and N on amine group delocalise into the π - electron system and increase the electron density of the ring, making it more attractive to electrophiles and makes it more likely to undergo further substitution, and so the aromatic ring is activated

Question 13

What is an electron withdrawing group on an aromatic ring and explain how it works

Answer 13

Substituent groups that “deactivate” the aromatic ring e.g. NO2 (nitro group). There are no lone pairs on the N in the nitro group, N and O are highly electronegative elements that withdraw electrons from the aromatic ring easily, and so ring is less attractive to electrophiles, and so less likely to undergo further substitution

Question 14

Which carbons on the aromatic ring do electron donating groups attach to

Answer 14

carbon-2, carbon-4 and carbon-6

Question 15

Which carbons on the aromatic ring do electron withdrawing groups attach to

Answer 15

carbon-3

Question 16

Fully explain why phenol is acidic

Answer 16

Phenol is acidic because when phenol release a H+ ion (proton), the charge on the oxygen of the phenoxide ion delocalises into the pi-electron system. This makes the phenoxide ion more stable, which means phenol can ionise/dissociate to form it readily

Question 17

Fully explain why phenol is more reactive than benzene

Answer 17

Phenol is more reactive than benzene because the lone pair of electrons in the p-orbital of the oxygen of the hydroxyl group delocalises into the pi-electron system. This increases the electron density of the aromatic ring which makes it more susceptible to electrophilic attack