EAS Mechanism Diagram Note

Nitration of Benzene — Stepwise Mechanism with SMILES:

Step 1 — Generation of Nitronium Ion:

$HNO_{3}$  +  $H_{2}SO_{4}$  →  $H_{2}NO_{3}^{+}$  +  $HSO_{4}^{-}$
$H_{2}NO_{3}^{+}$            →  $NO_{2}^{+}$   +  $H_{2}O$

SMILES of nitronium ion: [N+](=O)=O (formally: [O-][N+]#[O+])

Step 2 — Attack of $NO_{2}^{+}$ on Benzene (RDS):

Benzene: c1ccccc1 → Arenium ion (sigma complex): The $sp^{3}$ carbon at the attack site carries both $NO_{2}$ and H.

Label Table for Arenium Ion:

Feature	Description
$sp^{3}$ carbon	Carbon bonded to $NO_{2}$ and H simultaneously; not part of pi system
Positive charge	Delocalized over the remaining 5-carbon conjugated system (positions 1, 3, 5 relative to attack)
Loss of aromaticity	Ring is no longer fully conjugated — one $sp^{3}$ carbon breaks the conjugation
Driving force for Step 3	Restoring the 36 kcal/mol resonance energy by ejecting $H^{+}$

Step 3 — Loss of $H^{+}$ (Rearomatization):

Arenium ion → Nitrobenzene + $H^{+}$ (captured by $HSO_{4}^{-}$ → $H_{2}SO_{4}$ , regenerating acid catalyst)

Product SMILES: [O-][N+](=O)c1ccccc1 (nitrobenzene)

Wikimedia Mechanism Reference: Nitration of benzene — EAS mechanism with nitronium ion electrophile