what is electromeric effect

Electromeric effect is a molecular polarizability that occurs by an intramolecular electron displacement characterized by the substitution of one electron pair for another within the same atomic octet of electrons. It is a temporary effect that arises when the compound is subjected to an attacking reagent. The attacking reagent causes a complete shift of pi electrons, inducing polarity in the pi bonded atoms of an organic molecule. The effect is classified into two types, namely the +E effect and the -E effect, based on the direction in which the electron pair is transferred. The +E effect occurs when the shared electron pair is transferred towards the attacking reagent, while the -E effect occurs when the shared electron pair is transferred away from the attacking reagent. The electromeric effect is often considered along with the inductive effect as types of electron displacement. The concepts implied by the terms electromeric effect and mesomeric effect are absorbed in the term resonance effect.