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Organic Reaction Mechanisms

Follow electrons as bonds break, form, and rearrange.

Follow the cause1 / 3

An electron source attacks. A nucleophile or bond supplies an electron pair to an electron-poor centre.

electron movementsubstitution · pathway slower
Focus the idea
Electron arrows show a substitution or elimination pathwayA nucleophile approaches a carbon attached to a leaving group. The selected pathway is substitution and the pathway score is 59.CNu:LGNu: + R–LG → R–Nu + LG⁻
electron donorNu:
reaction centreCδ+
departing groupLG 45%
pathway59%

The nucleophile supplies an electron pair to the electrophilic carbon; a stronger nucleophile and better leaving group make this pathway easier.

Curved arrows track electron pairs, not atoms. The stage is a simplified SN2/E2 comparison; real selectivity also depends on substrate structure, solvent, temperature, and steric hindrance.

04 / PRACTICE

Make the chemistry yours.

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Answer from the model, then use the explanation to connect the particle picture to the chemical rule.

CHECK 1 / 3

Where should a curved arrow begin?