Chemistry A2 · Hydroxy compounds. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Phenol, C6H5OH, has an –OH group joined directly to a benzene ring. The ring and the –OH group change each other's behaviour.
Acidity: phenol is a weak acid, stronger than water and ethanol. When it loses H+, the negative charge on the oxygen of the phenoxide ion is delocalised into the ring, which makes the ion more stable. In the ethoxide ion the alkyl group pushes electrons towards the oxygen, so the charge is more concentrated and the ion is less stable.
Ring reactions: a lone pair on the oxygen is delocalised into the ring and raises its electron density. The ring attacks electrophiles much more easily than benzene does, so milder conditions are used and no catalyst is needed.
Using the benzene conditions for phenol (concentrated acids for nitration, AlBr3 for bromination). Phenol is far more reactive: dilute nitric acid and bromine water at room temperature are enough.
Answer: 360 cm3 of hydrogen
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