Bondline / Reactions

Bromination of benzene

FeBr₃ polarises Br₂ so the ring can attack it. The cationic intermediate then loses H⁺ and aromaticity returns. Benzene doesn’t react with Br₂ alone.

Aromatic substitution · 2 steps

Conditions

Br₂ with FeBr₃ (or Fe filings), room temperature, dark.

Mechanism in 2 steps

Red curly arrows show where each pair of electrons moves.

HBrBr+Fe−BrBrBrHBrBrFe−BrBrBr++
Step 1The ring attacks the outer bromine as the Br–Br bond breaks onto the FeBr₃.
HBrBrFe−BrBrBrBrHBrBrFeBrBr+++
Step 2FeBr₄⁻ delivers a bromide to the proton; the C–H electrons restore the aromatic ring.

About aromatic substitution reactions

Benzene keeps its stable aromatic ring by substituting rather than adding. An electrophile attacks, then a proton is lost to restore aromaticity.

Practise this mechanismDraw the curly arrows yourself and Bondline checks each one. Or add it to your notes and watch it in 3D.

Open in Bondline