A LITTLE LIGHTBULB MOMENT
Organic chemistry: mechanisms and functional groups
SN1 forms a carbocation first
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A leaving group leaves, then the nucleophile arrives late.
The idea behind the cue
SN1 proceeds in two steps: leaving group departure forms a carbocation, then nucleophile attack occurs. Because the carbocation is planar, stereochemistry is often mixed rather than cleanly inverted. Rearrangements can occur before capture.
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Short & simple
A leaving group leaves, then the nucleophile arrives late.
Acronym
DCPR — Dancing Cats Paint Ravioli.
Story
A celebrity exits a limo and leaves an open space. Fans rush in from either side, so the final pose can be either orientation. The middle step is a carbocation that can be rearranged if needed.
Connect the pieces
- D (Dancing) → Departure: The leaving group leaves first.
- C (Cats) → Carbocation: A carbocation intermediate forms after departure.
- P (Paint) → Planar: The carbocation is planar, so attack can occur from either face and stereochemistry is often mixed.
- R (Ravioli) → Rearrangement: Hydride or alkyl shifts can happen before nucleophilic capture.
- Dancing · Departure: The leaving group leaves first.
- Cats · Carbocation: A carbocation intermediate forms after departure.
- Paint · Planar: The carbocation is planar, so attack can occur from either face and stereochemistry is often mixed.
- Ravioli · Rearrangement: Hydride or alkyl shifts can happen before nucleophilic capture.
Know the limits
Favored by substrates that can form stable carbocations; rearrangements are possible only in the carbocation step.
Further reading · OpenStax science and mathematics textbooks ↗Check your understanding
What is the key intermediate in an SN1 reaction?
A. A carbanion
B. A radical pair
C. A bridged epoxide
D. A carbocation
Reveal explanation
A carbocation
SN1 means substitution nucleophilic unimolecular, with a carbocation intermediate formed after leaving-group departure.