Chemistry 4.3 - Phenols

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Is phenol a strong or weak acid?
Weak acid.
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The ion produced when phenol reacts with water is called the...
Phenoxide ion.
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How does phenol act as a weak acid?
It donates a proton. The lone pair of the oxygen then overlaps with the delocalised pi electron system to form an EXTENDED delocalised pi electron system.
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How does this extended delocalised pi electron system affect the C-O bond?
The bond is shorter and stronger, making bond fission harder.
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Place the three molecules in order of weakest and strongest acid: phenol, ethanoic acid and ethanol.
Ethanol = weakest acid. Ethanoic acid = strongest acid.
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Test to distinguish between a c.acid and phenol?
Add sodium/sodium hydrogen carbonate as c.acids will produce effervescence.
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Stability of the phenoxide ion.
The stability of the phenoxide ion is increased by the delocalisation of the negative charge on the ion.
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The OH group of the phenol activates the ring to attack by electrophiles. Why?
One of the lone pairs on the oxygen atom overlaps with the delocalised pi electron system increasing the electron density around the ring. Each position is activated towards attack, BUT the 2, 4, and 6 positions are activated to a greater extent.
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What are the two reactions of phenol that must be known?
1. Bromine water. 2. Ethanoyl chloride.
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Phenol will react with bromine water. How is the bromine molecule polarised and what colour ppt is formed?
The increased electron density in the ring polarises the bromine molecule. A white ppt is produced (solution changes from orange to white and so could be used as a test for phenols).
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Phenols can act as nucleophiles. How?
By the use of a lone pair on the oxygen.
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This reaction is difficult for phenols and so a base, such as pyridine, is used. Why is it difficult?
The electron pair is already overlapping with the delocalised pi electron system. Pyridine therefore speeds up the rate of reaction.
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There is a disadvantage of the reaction between phenol and ethanoyl chloride. What molecule can be used as a replacement?
Ethanoyl chloride is an expensive reagent. Instead, ethanoic anhydride can be used.
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What test for phenol gives a purple solution?
The use of iron chloride.
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Other cards in this set

Card 2

Front

The ion produced when phenol reacts with water is called the...

Back

Phenoxide ion.

Card 3

Front

How does phenol act as a weak acid?

Back

Preview of the front of card 3

Card 4

Front

How does this extended delocalised pi electron system affect the C-O bond?

Back

Preview of the front of card 4

Card 5

Front

Place the three molecules in order of weakest and strongest acid: phenol, ethanoic acid and ethanol.

Back

Preview of the front of card 5
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