Find the electron source
Start at a lone pair or a bond that can supply an electron pair.
Electron-flow practice
Reaction Mechanism Trainer
Choose the electron source and destination for each curved arrow. The trainer checks where the electrons start, where they finish and how the structure changes.
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Choose a mechanism course
Review the prediction rules first, then complete each mechanism one elementary step at a time.
Prediction rules
Find the electron-poor destination
Finish at an atom or bond that can accept the electrons without violating the intended step.
Check acid–base roles
Identify the base, the acidic proton and the bond whose electrons return to the conjugate base.
Track resonance and bond order
When a π bond moves, update adjacent bond orders and formal charges together.
Consider steric access and leaving groups
Substitution and elimination depend on access to the reacting carbon, β-hydrogen alignment and leaving-group ability.
Keyboard operation
Tab moves through the structure. Enter selects a source or destination. Arrow keys move between hotspots. Escape clears the pending selection.
Select a source, then a destination. Add every arrow required for this elementary step.