Electromeric Effect (+E / −E) (+E: π electrons shift toward attacking electrophile; −E: away from nucleophile)
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+E: π electrons shift toward attacking electrophile; −E: away from nucleophile
What each symbol means
| Symbol | What it stands for |
|---|---|
| +E | π bond donates toward electrophile as it approaches |
| −E | π bond polarizes away from nucleophile |
When to use this
Transient, reagent-dependent; disappears when reagent leaves. Distinct from permanent inductive/resonance.