Question

Which of the following exhibit electromeric effect-
A.alkane
B.aldehyde
C.alkyl halides
D.alkyl amines

Answer 1

An intramolecular electron displacement defined by the replacement of one electron pair for another inside the same atomic octet of electrons causes the electromeric effect, which is a molecular polarizability effect. As a kind of electron displacement, the electromeric effect is frequently discussed alongside the inductive effect.

Complete solution:
The Electromeric effect is the development of a dipole in a molecule of an organic compound as a result of the full transfer of shared pi electron pairs to one of the atoms under the action of an attacking reagent.
In organic molecules with at least one multiple bond, this effect can be seen. When an attacking reagent comes into contact with the atoms in this multiple bond, one pi bonding pair of electrons is fully transferred to one of the two atoms.
The electromeric effect is a transient effect that lasts as long as the attacking reagent is present and the organic molecule is exposed to it. The polarised molecule returns to its natural state after the attacking reagent is withdrawn from the solution.
The +E effect and the -E effect are two forms of electromeric effects. The direction in which the electron pair is exchanged is used to classify them.
+E (plus effect)
When the pi bond's electron pair is pushed towards the attacking reagent, this result happens. When acid is added to alkenes, the +E effect is visible. The attacking reagent binds to the atom that received an electron pair during the transfer. When the attacking reagent is an electrophile and the pi electrons are transported to the positively charged atom, the +E effect occurs.
-E effect
When the electron pair of the pi bond is pushed away from the attacking reagent, the -E effect occurs. The attacking reagent binds to the molecule's positively charged atom, i.e. the atom that lost an electron pair during the transfer. When the attacking reagent is a nucleophile and the pi electrons are moved to an atom that the attacking reagent will not bind with, the -E effect occurs.

Hence option b is correct.

Note:
Although some individuals refer to it as an effect caused by the presence of a reagent such as an electrophile or a nucleophile, the International Union of Pure and Applied Chemistry (IUPAC) does not describe it as such. The phrases electromeric effect and mesomeric effect are no longer used in standard textbooks and are considered outdated. The word resonance effect absorbs the notions suggested by the terms electromeric effect and mesomeric effect. Curved arrows, which indicate the electron shift, can be used to depict this phenomenon.