AC5: Phenols

Question 1

How does phenol differ from benzene, structurally

Answer 1

Phenol has an OH group attached to the aromatic ring

Question 2

What state is phenol at room temp

Answer 2

Solid

Question 3

Why is phenol only slightly soluble in water

Answer 3

It can form hydrogen bonds from the OH group but it has a much bigger non-polar hydrocarbon which cannot form hydrogen bonds

Question 4

Is the solution of phenol in water acidic or alkaline

Answer 4

Slightly acidic

Question 5

Is phenol a strong or weak acid

Answer 5

Weak

Question 6

With phenol being a weak acid, does it react with weak or strong bases

Answer 6

Strong bases

Question 7

What is a good test to tell the difference between phenols and carboxylic acids

Answer 7

Add carbonate since phenols are such weak acids they don’t react with carbonate so produce no fizzing whereas carboxylic acids do fizz

Question 8

Do phenols or benzene react much more easily via electrophilic substitution

Answer 8

Phenols

Question 9

Why do phenols undergo electrophilic substitution reactions much more easily than benzene

Answer 9

• A lone pair of electrons on oxygen is delocalised into the pi system of the ring which increases the electron density in the aromatic ring making it more attractive to electrophiles
• So the OH is therefore said to be an electron donating group

Question 10

When substituting on a phenol, what 3 positions on the ring does the substitution usually occur

Answer 10

• 2, 4, 6

Question 11

What is the comparative statement: benzene and bromine don’t need a solvent to react

Answer 11

Whereas phenol and bromine need water

Question 12

What is the comparative statement: benzene and bromine need a halogen carrier catalyst to react

Answer 12

Whereas phenol and bromine don’t need a catalyst

Question 13

What is the comparative statement: when benzene and bromine react 1 hydrogen is easily replaced

Answer 13

Whereas when phenol and bromine react 3 hydrogens are easily replaced

Question 14

What is need to nitrate a phenol

Answer 14

Aqueous nitric acid

Question 15

How is nitrating phenol different from nitrating benzene

Answer 15

When nitrating benzene you need concentrated nitric acid and concentrated sulfuric acid where when nitrating phenol you only need aqueous nitric acid

Question 16

What 2 groups when bonded to an aromatic ring are called electron donating groups

Answer 16

• OH
• NH2

Question 17

Why is OH or NH2 known as electron donating groups when attached to an aromatic ring

Answer 17

Because the oxygen or the nitrogen has a lone pair that can delocalise into the pi-system of the ring, increasing it’s electron density

Question 18

What 2 important effects on electrophilic substitution reactions do electron-donating groups have

Answer 18

• They increase the reactivity of the ring - increased electron density makes the ring more attractive to electrophiles
• They direct substitution reactions to take place at the 2,4,6 positions

Question 19

When bonded to an aromatic ring what is the electron withdrawing group

Answer 19

NO2

Question 20

What effects on electrophilic substitution reactions do electron withdrawing groups have

Answer 20

• They decrease the reactivity of the ring since they lower the electron density which makes the ring less attractive to electrophiles
• If they are strongly deactivated (NO2) they direct substitution reactions to take the 3 and 5 position