Mechanism of Nitration

The nitration of benzene follows the electrophilic substitution mechanism. You need to be able to write every step.Forming the electrophile. Concentrated sulfuric acid reacts with concentrated nitric acid to make the nitronium ion, NO₂⁺:HNO₃ + H₂SO₄ → NO₂⁺ + HSO₄⁻ + H₂OStep 1. A curly arrow is drawn from the delocalised ring to the nitrogen atom of NO₂⁺: a pair of delocalised electrons forms a new C-N bond. The carbon that bonds to N now holds both H and NO₂ and is no longer part of the delocalised system. The intermediate is drawn as a horseshoe covering the other five carbon atoms, with a positive charge inside it. The horseshoe must open towards the carbon bonded to H and NO₂.Step 2. A curly arrow goes from the C-H bond back into the ring. The electrons restore the full delocalised ring and a proton (H⁺) is lost, giving nitrobenzene.Regenerating the catalyst. The H⁺ released reacts with the hydrogensulfate ion:H⁺ + HSO₄⁻ → H₂SO₄so the sulfuric acid is regenerated and acts as a catalyst.Common mistakes: starting the first arrow from a single carbon instead of the ring, pointing it at an oxygen of NO₂⁺, and drawing the horseshoe too big or with no + charge.