Bondline / Reactions

Epoxide ring opening (base)

Under basic conditions a nucleophile opens the strained three-membered ring by SN2 at the less hindered carbon.

Substitution · 2 steps

Conditions

NaOMe in MeOH (or other nucleophiles: OH⁻, RNH₂, RMgBr). Under acid, attack moves to the more substituted carbon.

Mechanism in 2 steps

Red curly arrows show where each pair of electrons moves.

O−OOO−HO++
Step 1Methoxide attacks the less hindered CH₂ carbon; ring strain is released as the C–O bond breaks.
OO−HOOOHO−MeOH++
Step 2The alkoxide is protonated by the solvent.

About substitution reactions

In a substitution, a nucleophile replaces a leaving group on a saturated carbon. Whether it happens in one step (SN2) or through a carbocation (SN1) depends on the substrate, the nucleophile and the solvent.

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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