Mechanism marks are given for arrows, not for products. Almost all lost marks come from an arrow that starts in the wrong place.
The one rule
Arrows start at electrons, a lone pair or a bond, never at a positive charge. Ask the tutor to mark every electron source on the board before drawing a single arrow.
The four families
- 1Nucleophilic substitution (SN1 vs SN2: decide from the substrate first)
- 2Elimination (E1, E2, and why base strength picks the path)
- 3Electrophilic addition to alkenes
- 4Electrophilic aromatic substitution
Checking your own work
- Count charges on both sides. They must balance.
- Every arrow head must land on an atom or a bond, never in space.
- Name the intermediate out loud. If you can't name it, it's probably wrong.
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