🧬 Organic Lab Level 6 · HL

⚙️ Mechanism Setup
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Click source atom, then target to draw curly arrow
Reaction Mechanisms ● Select a mechanism
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Organic Reaction Mechanisms

  • Curly arrows show electron pair movement: from electron-rich → electron-poor
  • Arrow starts from lone pair or bond, ends at atom or between atoms (new bond)
  • Nucleophile: electron pair donor (lone pair or π electrons)
  • Electrophile: electron pair acceptor (δ+ atom)
  • Leaving group: departs with the bonding pair of electrons
  • Number of curly arrows = number of electron pair movements in that step

SN2 — Bimolecular Nucleophilic Substitution

  • One step: nucleophile attacks as leaving group departs simultaneously
  • Rate = k[substrate][nucleophile] — second order overall
  • Backside attack → inversion of configuration (Walden inversion)
  • Favoured by: primary substrates, strong nucleophiles, polar aprotic solvents
  • Two curly arrows: Nu: → C and C–LG → LG:

SN1 — Unimolecular Nucleophilic Substitution

  • Step 1: Leaving group departs → carbocation intermediate forms (rate-determining)
  • Step 2: Nucleophile attacks the carbocation
  • Rate = k[substrate] — first order overall
  • Planar carbocation → racemization (attack from both sides)
  • Favoured by: tertiary substrates, weak nucleophiles, polar protic solvents

Electrophilic Addition

  • Step 1: Electrophile (e.g., H–Br) attacks the C=C double bond. π electrons form new σ bond with H⁺
  • Step 2: Br⁻ nucleophile attacks the carbocation intermediate
  • Follows Markovnikov's rule: H adds to the carbon with more H atoms
  • Most common with alkenes + hydrogen halides (HBr, HCl) or halogens (Br₂)
  • Two curly arrows in step 1: C=C → H and H–Br → Br