Arrow rules that never change
A double-headed curved arrow moves an electron pair. Start from a source of density—a lone pair or a bonding pair—and end where that pair creates a new bond or a lone pair on an atom. Single-barbed “fishhook” arrows (one electron) belong to radical chapters; do not mix them into polar SN/E mechanisms.
- Never draw an arrow that invents electrons from nowhere.
- Never end an arrow in empty space; it must land on an atom or a bond-forming region your instructor accepts.
- Charge and octet bookkeeping must stay consistent after each step.
If a step looks “magic,” you skipped an intermediate your course requires—proton transfer, carbocation, or tetrahedral intermediate.
SN, E, and addition patterns to memorize with arrows
Build a small set of arrow templates, then vary the substrate:
- SN2 — nucleophile lone pair → electrophilic carbon; C–LG bond → leaving group (concerted).
- SN1 — C–LG breaks first to a carbocation; then nucleophile → carbocation carbon.
- E2 — base → β-H; C–H bond → forming π bond; C–LG → leaving group (often shown as a concerted set).
- Electrophilic addition — π bond → electrophile; then nucleophile captures the carbocation (or follows the specific mechanism your text uses).
When substitution vs elimination is the real question, pair this practice with SN1 vs SN2 decision factors so arrows and pathway choice stay linked.
Common curved-arrow mistakes on exams
Graders see the same errors repeatedly:
- Arrows starting from the positive atom instead of the nucleophilic source.
- Showing SN2 inversion verbally but drawing front-side attack.
- Skipping the carbocation in SN1, then wondering why rearrangements never appear.
- Using acid/base arrows that create impossible charge states.
- Drawing the product first and reverse-engineering arrows that do not match kinetic steps.
Fix the habit: cover the answer key, redraw every arrow from reagents, then uncover and mark only the steps you missed. Speed comes after accuracy.
A weekly drill loop that sticks
Spend 20–30 minutes most days on one reaction family, then mix types twice a week. For each problem: predict pathway, draw arrows, write major/minor, check against a worked solution, and note one rule you violated. Visual walkthroughs—major vs minor, key points, full electron pushing—train the “why” better than flashcards of reaction names alone.
OrgoMech shows step-by-step curved-arrow mechanisms for core library reactions (substitutions, eliminations, additions, and more) so you can compare your drawing to a clear sequence after you attempt it yourself.
Download OrgoMech on the App Store
Want guided electron-pushing practice on your phone? OrgoMech is free to download on the App Store. Browse mechanisms on the free tier; OrgoMech Pro unlocks full access to the predictor, library, and study features. Read the privacy policy for App Store details.
Educational study aid only — not a homework cheat, not exam fraud, and not a substitute for your course or instructor.
Frequently asked questions
How do I get better at curved arrows fast?
Daily full-mechanism redraws on a small set of reaction types beat marathon cramming. Always attempt arrows before looking at any answer, then expand to mixed problem sets.
Do double-headed arrows move one electron or two?
A standard double-headed curved arrow represents a pair of electrons. One-electron (fishhook) arrows are for radical mechanisms.
Should I memorize products or mechanisms first?
Learn the mechanism pattern first; products follow from the arrows. Product-only memorization collapses when reagents or stereochemistry change on the exam.
Does OrgoMech show electron pushing?
Yes—step-by-step curved-arrow mechanisms for reactions in the library. Free to download; Pro unlocks full access. Use it to check your practice, not to copy graded work.