The following effect is known as___

Electromeric effect is a temporary effect in which a shared pair of electrons ($\mathrm{\pi }$-electron pair) is completely transferred from a double or a triple bond to one of the atoms joined by the bond at the requirement of attacking species. The Electromeric effect is represented by symbol $\mathrm{E}$, and is said to be $+ \mathrm{E}$ when the displacement of $\mathrm{\pi }$ electrons is away from the atom or group, and $- \mathrm{E}$ when displacement of $\mathrm{\pi }$ electrons are towards the atom or group. If the multiple bond is present between two different atoms, the electron shift will take place in the direction of the more electronegative atom. Hence, the following effect is known as Electromeric effect.