BRAINCAKE2- and 4-Directing Groups
Groups that donate electron density to the benzene ring, such as -OH and -NH2, are 2- and 4-directing.
Why they are electron-donating
The oxygen in -OH and the nitrogen in -NH2 each have a lone pair in a p-orbital that overlaps with the ring's π-system. The lone pair is partially delocalised into the ring, increasing its electron density. The increase is greatest at positions 2, 4 and 6, so electrophiles substitute there.
Activation
Because the ring is more electron-rich, these groups make it more reactive than benzene. Reactions go under milder conditions, and several substitutions often happen at once.
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More in Benzene
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All 16 lessons in Benzene · All OCR A-level Organic Chemistry topics