Bondline / Reactions

E2 elimination

A strong base removes a proton next to the leaving group as the C=C forms and the leaving group departs, in one step. The H and leaving group must be anti-periplanar.

Elimination · 1 step

Conditions

Strong, often bulky base (e.g. EtO⁻, t-BuO⁻), heat. Rate = k[RX][base].

Mechanism

Red curly arrows show where each pair of electrons moves.

O−HBrOHBr−+++
MechanismEthoxide takes a β-hydrogen; the C–H electrons form the π bond while bromide leaves.

About elimination reactions

In an elimination, a proton and a leaving group are removed from neighbouring carbons and a C=C forms. Strong bases and heat favour elimination over substitution.

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

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