Please explain +E and -E electromeric effects with examples.

1 Answer

Answer:

The electromeric effect is the movement of electrons from one atom to another as a reagent attacks a π bond.

Explanation:

+E EFFECT

If the attacking species is an electrophile, the π electrons are transferred towards the positively charged atom. This is the +E effect.

An example is the protonation of ethene. When the H⁺ comes near the double bond, the bond is polarized towards the proton.

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-E EFFECT

If the attacking reagent is a nucleophile, the electrons are transferred away from the attacking reagent and into the π system. This is the –E Effect.

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The term “electromeric effect” is somewhat outdated. We are more likely now to use words like “Use curved arrow notation to show the movement of electrons during the reaction”.