The nitronium ion NO2+ approaches the benzene ring A partial bond forms between the ring and the NO2+, the electron density coming from the ring system An intermediate (the Wheland intermediate) forms, where the attacked carbon is sp3 hybridised and the delocalised electron system in the ring is broken The hydrogen ion that is to be lost must be accepted by the HSO4- ion which moves towards the intemediate HSO4- accepts the proton, reforming sulphuric acid The electrons that bound the hydrogen return to the p-system in the ring, reforming the delocalised system and restoring aromaticity.

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