Paper 3A Part 2
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.If the compound doesn’t have a OH bond directly but still has an OH group it is classed as an ______, not a ______
alcohol, not a phenol
.Phenol is less soluble in water than alcohols, why?
due to its non-polar benzene ring
When dissolved in water, phenol partially dissociates to form what?
a phenoxide ion and a proton
As phenol only partially dissociates it is ______, other phenols also act as ________
a weak acid (pH4-6)weak acids
.Ethanol doesn’t react with sodium hydroxide (strong ___) or sodium carbonate (weak ___)
basebase
Phenols and carboxylic acids will react with ____________________ (like aqueous sodium hydroxide)
solutions of strong bases
carboxylic acids are strong enough to react with a weak base like sodium carbonate, you would observe what?
a gas/bubbles
Draw the mechanism for phenol and sodium hydroxide
check notes or internet
Draw the mechanism for phenol and sodium
check notes or internet
Describe the bromination of phenols?
.Phenol reacts with aqueous solution of bromine (bromine water) .A halogen carrier is not required and the reaction can be carried out at room temperature
Draw the mechanism of phenol and Br2
Check notes or internet
What does the bromination of phenol look like?
This reaction decolourises bromine water and forms a white precipitate
Why does phenol react more readily with bromine than benzene?
.One of the lone pairs of electrons on the p orbital of the O atom in the OH is partially delocalised into the ring.This increases the electron density.The electrophile becomes more polarised
Describe the nitration of phenol
.Phenol readily reacts with dilute nitric acid at room temperature.It does not need halogen carrier.Makes with 2-nitrophenol or 4-nitrophenol and water
Draw the nitration of phenol mechanism
check notes or internet
Many aromatic compounds can undergo a second substitution, what is this called?
a di-substitution
What is the directing effect?
The presence of substituted groups on a benzene ring will have an effect on the substitution of further groups – this is known as the directing effect
Substituted groups can be classified by the effect they have on the electron density of the ring, what are the classifications?
• Electron donating – increases the electron density- Withdrawing electrons – decrease electron density
What are electron donating substitition groups also known as, why?
.Side chains that increase electron density allow electrophiles to react faster than with benzene, so are ‘activating’ products
Give an example of an electron donating substitution group
.OH – O lone pair orbitals overlap with delocalised ring.NH2 – N lone pair orbitals overlap with delocalised ring
Where do electron donating groups promote substitution?
.They increase the electron density at positions 2, 4, and 6.So electrophiles are more likely to react at these positions.The group directs substitution to positions 2, 4, and 6.2, 4-directing.The weaker position at 3 and 5 are rarely substituted
What are electron withdrawing substitition groups also known as, why?
.Side chains that decrease electron density slow electrophile reactions compared to benzene, so are ‘deactivating’ groups
Give an example of an electron withdrawing substitution group
.NO2 – O is more electronegative, drawing electrons away from the delocalised ring
Where do electron withdrawing groups promote substitution?
.It withdraws electron density at position 2, 4, and 6 – meaning that electrophiles are unlikely to react at these positions.The group directs substitutes to position 3.3- directing.The weaker positions at 2 and 4 are rarely substituted