Every organic chemistry mechanism is a sequence of electron movements. There are only a handful of moves the electrons can make. Once you can name them, every named reaction starts looking like a sentence built from the same vocabulary.
The seven moves
- 1Proton transfer (acid-base) — a base takes a proton, a conjugate acid forms.
- 2Nucleophilic attack — a lone pair or pi-bond attacks an electrophilic carbon.
- 3Loss of leaving group — a bond breaks heterolytically, electrons go with the leaving group.
- 4Carbocation rearrangement — hydride or alkyl shift to form a more stable cation.
- 5Pi-bond formation (elimination) — two atoms lose a leaving group + proton, forming a double bond.
- 6Pi-bond breakage (addition) — double bond opens, two new sigma bonds form.
- 7Tautomerization — proton + double bond shift, isomerizing keto/enol or imine/enamine.
Mapping named mechanisms to the seven moves
| Named mechanism | Composition |
|---|---|
| SN2 | Nucleophilic attack + loss of leaving group (concerted) |
| SN1 | Loss of leaving group → nucleophilic attack |
| E2 | Proton loss + leaving-group loss + pi-bond formation (concerted) |
| E1 | Loss of leaving group → proton loss + pi-bond formation |
| Markovnikov addition | Pi-bond breakage → proton transfer + nucleophilic attack |
| Acid-catalyzed addition to carbonyl | Proton transfer → nucleophilic attack → proton transfer |
| Aldol | Proton transfer → nucleophilic attack → proton transfer |
| Claisen | Proton transfer → nucleophilic attack → loss of leaving group |
| Wittig | Nucleophilic attack → pi-bond formation + loss of leaving group |
| Friedel-Crafts | Loss of leaving group (with Lewis acid) → nucleophilic attack → proton loss |
How to use this in practice
Step 1 — when you see a new mechanism, decompose it
Every time your textbook introduces a new named mechanism, write out the sequence of the seven moves underneath. Within 3 weeks, every new mechanism becomes 'oh, it's a proton transfer plus nucleophilic attack' instead of an unfamiliar named entity.
Step 2 — drill by move type, not by name
Most organic chem flashcard decks are organized by reaction name. Reorganize yours by move type. AceNotes' free orgo decks let you tag cards by move (proton transfer, nucleophilic attack, etc.) and drill by tag — practice 30 nucleophilic attacks across different reactions and you'll start recognizing them in any context.
Step 3 — predict products by sequencing moves
On exams, when you see a starting material and reagents, ask: 'what's the first move?' Then 'what's the next?' Sequencing the moves correctly almost always lands you on the correct product, even if you've never seen the exact reaction before.
Common mistakes when learning mechanisms
- Memorizing without practicing arrow-pushing. Mechanisms have to be drawn, not recognized.
- Skipping the intermediate steps. Carbocations, tetrahedral intermediates — they're worth points and they're how you check your work.
- Treating each new chapter's mechanisms as unrelated to last chapter's. They're built from the same moves.
- Drilling without conditions. The same starting material gives different products under different conditions — your decks should pair material with conditions.
- Studying mechanisms only before exams. They compound. The students who drill 15 minutes a day always outperform the students who cram.
Drill organic chemistry mechanisms by pattern, free, on AceNotes.
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