AC5: Phenols
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How does phenol differ from benzene, structurally
Phenol has an OH group attached to the aromatic ring
What state is phenol at room temp
Solid
Why is phenol only slightly soluble in water
It can form hydrogen bonds from the OH group but it has a much bigger non-polar hydrocarbon which cannot form hydrogen bonds
Is the solution of phenol in water acidic or alkaline
Slightly acidic
Is phenol a strong or weak acid
Weak
With phenol being a weak acid, does it react with weak or strong bases
Strong bases
What is a good test to tell the difference between phenols and carboxylic acids
Add carbonate since phenols are such weak acids they don’t react with carbonate so produce no fizzing whereas carboxylic acids do fizz
Do phenols or benzene react much more easily via electrophilic substitution
Phenols
Why do phenols undergo electrophilic substitution reactions much more easily than benzene
• 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
When substituting on a phenol, what 3 positions on the ring does the substitution usually occur
• 2, 4, 6
What is the comparative statement: benzene and bromine don’t need a solvent to react
Whereas phenol and bromine need water
What is the comparative statement: benzene and bromine need a halogen carrier catalyst to react
Whereas phenol and bromine don’t need a catalyst
What is the comparative statement: when benzene and bromine react 1 hydrogen is easily replaced
Whereas when phenol and bromine react 3 hydrogens are easily replaced
What is need to nitrate a phenol
Aqueous nitric acid
How is nitrating phenol different from nitrating benzene
When nitrating benzene you need concentrated nitric acid and concentrated sulfuric acid where when nitrating phenol you only need aqueous nitric acid
What 2 groups when bonded to an aromatic ring are called electron donating groups
• OH • NH2
Why is OH or NH2 known as electron donating groups when attached to an aromatic ring
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
What 2 important effects on electrophilic substitution reactions do electron-donating groups have
• 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
When bonded to an aromatic ring what is the electron withdrawing group
NO2
What effects on electrophilic substitution reactions do electron withdrawing groups have
• 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