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Organic Chemistry I · Problem type
Where the nucleophile opens an epoxide
Use this for “2,2-Dimethyloxirane reacts with NaOCH₃ in CH₃OH. Which ring carbon does the methoxide bond to?”
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Which ring carbon does the nucleophile bond to?
Tap a card, then tap its group.
A strong nucleophile goes where there is room; in acid the nucleophile goes where the + charge sits.
Assumptions
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Every card opens 2,2-dimethyloxirane: one ring carbon holds two CH₃ groups (more substituted), the other is a CH₂ (less substituted).
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The three-membered ring is strained, so a strong nucleophile can open it although the O⁻ it pushes out is a poor leaving group.
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A strong nucleophile, charged or basic, attacks by SN2 at the less hindered carbon; the O⁻ left behind takes H⁺ in the workup.
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In acid the O takes H⁺ first; the more substituted carbon carries more of the + charge, so a weak nucleophile attacks it there, from the back.
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