Directing effects in nitration template

Para attack on toluene gives an arenium ion with one tertiary resonance form; meta attack on nitrobenzene keeps the + charge away from the carbon bearing N⁺.

Mechanism step by step

CH₃ directs ortho/para, NO₂ directs meta: compare where the + charge of the arenium ion can sit

1. Toluene: para attack – The para carbon attacks NO₂⁺
2. A 3° cation form – One resonance form puts + on the carbon bearing CH₃
3. Nitrobenzene: meta attack – The + charge goes to C2, C4, C6, never to C–NO₂
4. Why not para? – Para attack would put + on the carbon bearing N⁺: avoided

Key points

• Alkyl, –OH, –OR, –NH₂ and –NHCOR activate the ring and direct ortho/para (–OH and –NH₂ donate a lone pair to the cation).
• –NO₂, –CN, –CHO, –COR, –COOH and –SO₃H deactivate and direct meta.
• Halogens are the exception: deactivating (–I) but ortho/para-directing (lone-pair donation).
• Toluene nitrates about 25 times faster than benzene (about 59% ortho, 37% para, 4% meta); nitrobenzene needs fuming HNO₃ and about 100 °C to give 1,3-dinitrobenzene.

Drawn with 105 atoms, 11 arrows, 6 shapes – every one editable in MolDraw.

Sources

• Clayden, Greeves & Warren, Organic Chemistry, 2nd ed., OUP 2012, ch. 21 Textbook
• Smith, March's Advanced Organic Chemistry, 8th ed., Wiley 2020, ch. 11 Textbook