🔄 SN1 vs SN2 – Mechanism, Substrate, and Speed
Substitution reactions—SN1 and SN2—are at the heart of DAT organic chemistry. You’ll be tested on:
Reaction steps
Stability of intermediates
Effects of solvent, nucleophile, and leaving group
Predicting major product
Let’s decode both mechanisms side-by-side so you can score higher and answer faster.
🔬 Reaction Summary Table
| Feature | SN1 | SN2 |
|---|---|---|
| Mechanism Steps | Two (carbocation intermediate) | One (concerted backside attack) |
| Rate-Determining | Substrate only | Substrate + nucleophile |
| Preferred Substrate | 3° > 2° | 1° > 2° |
| Nucleophile | Weak (H₂O, ROH) | Strong (OH⁻, CN⁻) |
| Leaving Group | Stable required | Stable required |
| Solvent Type | Polar protic (H₂O, alcohols) | Polar aprotic (DMSO, acetone) |
| Stereochemistry | Racemic (loss of configuration) | Inversion (Walden inversion) |
🧠 Mnemonic: “SN1 Is Slow and Solo”
SN1 = Stepwise, Stable carbocation, Solvolysis
SN2 = 2 players (nucleophile + substrate) in 1 move
✅ Use this to quickly remember key differences.
🔁 Stereochemistry Differences
SN1: Loss of stereochemistry → racemic mixture
SN2: Stereospecific → 100% inversion of configuration
🧠 SN2 = SNiPer Attack (direct hit from behind).
🧪 DAT Practice Tip: When to Choose SN1 vs SN2
Look for this on test day:
| If you see... | Think... |
|---|---|
| Tertiary substrate + protic solvent | SN1 |
| Primary substrate + strong nucleophile | SN2 |
| Acetone or DMSO as solvent | SN2 |
| Racemic mixture formed | SN1 |
| Inversion of configuration | SN2 |
📈 DAT-Style Practice Question
Q: A primary alkyl halide reacts with NaCN in acetone. What is the mechanism?
✅ A: SN2 – strong nucleophile and aprotic solvent
🎯 DAT Strategy Tips
✅ Know which substrates favor SN1 vs SN2
✅ Practice drawing curved arrows and mechanisms
✅ Memorize stereochemistry outcomes
✅ Use solvent type as a tiebreaker clue
✅ Don’t confuse with elimination (E1/E2) – check base strength and heat
Get visuals & tables at kingofthecurve.org/studyscience
🚀 Call-to-Action
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Download the KOTC App for:
SN1 vs SN2 comparison drills
Nucleophile/leaving group flashcards
Reaction practice quizzes
Curve Coins to boost your ranking
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Frequently Asked Questions (FAQs)
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Aim for 4-6 focused hours, ensuring you incorporate breaks to avoid burnout.
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Practice mindfulness techniques, take practice exams under realistic conditions, and maintain a balanced lifestyle.
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