Question

If the attacking reagent is a nucleophile, the electrons are transferred away from the attacking reagent and into the system. This is known as:
A. E effect
B. +E effect
C. R effect
D. +R effect

Answer 1

Hint: This effect is observed only in unsaturated compounds. In this effect, a dipole is formed in the molecule because of the complete sharing of pi electrons to the atom under the presence of the attacking group.

Complete step by step answer:
The electromeric effect is classified as the +E effect and - E effect.
When the nucleophile is exposed to the molecule having a double bond, the electron pair present in the pi bond proceeds away from the attacking group. Hence the attacking group gets attached to the atom carrying a positive charge as the atom loses its electron pair during the transfer.
The –E effect is seen when the attacking group is a nucleophile and the pi electrons are moved to the atom where the attacking group will not join.
Example: Addition of nucleophiles group to the carbonyl compound as shown below.

Here, the nucleophile cyanide ion attacks the carbonyl carbon to form a product.
This reaction shows –E effect.
Thus, if the attacking reagent is a nucleophile, the electrons are transferred away from the attacking reagent and into the system. This is known as the –E effect.
Therefore, the correct option is A.


Note:
The electromeric effect remains as long the attacking group is present and close to the organic compound. When the attacking group is removed, the polarized molecule changes to its original form.