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Solutionsmeta Directors

1. Meta groups

Predict the result of the following reactions:

Six reactions: bromination of nitrobenzene, sulfonation of aniline, nitration of acetophenone, alkylation of N-methylaniline with cyclohexene in H₂SO₄, chlorination of methyl benzoate and alkylation of benzamide with cyclobutylmethanol and BF₃
Meta products: m-bromonitrobenzene, the anilinium salt of m-aminobenzenesulfonic acid, m-nitroacetophenone, the salt of N-methyl-3-cyclohexylaniline, methyl m-chlorobenzoate and 3-cyclopentylbenzamide

In acidic medium amines are protonated, and the resulting ammonium group is deactivating and meta-directing. The cyclobutylmethyl cation rearranges to cyclopentyl before attacking the ring.

2. Never "favors"

Explain why it is wrong to say that the nitro group "favors" meta substitution.

The nitro group disfavors substitution at all positions. It simply disfavors it less at meta, because in the ortho and para benzenonium ions one resonance form places the positive charge next to the positive nitrogen of the nitro group. Meta substitution is always slower than in benzene.

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