Question

Electromeric effect in an organic compound is
A.Temporary effect
B.Permanent effect
C.Temporary permanent effect
D.None of these

Answer 1

Hint:Electromeric effect depends upon the attacking reagent and does not exist in the absence of attacking external reagent. Electronic displacement in covalent bonds of organic compounds can take place by inductive, hyperconjugation, electronic or resonance effect.

Complete step by step answer:
- Electronic displacement in covalent bonds of organic compounds can take place by inductive, hyperconjugation, electronic or resonance effect. Inductive effect is the permanent displacement of electrons in a bond towards the more electronegative element from the less electronegative element. This effect provides polarity to the molecule in ground state. The property of electron withdrawal by an atom or group is the $$-\text{I}$$ effect and that of a donation is called $$\text{ + I}$$ effect. Inductive effect is also known as transition effect. Magnitude of inductive effect decreases with distances.
- Electromeric effect is the temporary shifting of $$\pi$$ electrons of the multiple bond system toward the more electronegative element in the presence of an attacking external reagent. If the attacking external reagent is an electrophile then the effect is $$+\text{E}$$ effect and if a nucleophile is an attacking external reagent than said to be $$-\text{E}$$ effect. Resonance effect involves permanent delocalization of $$\pi$$ electrons in a conjugated system. For this intermediate structures are formed which are known as resonating structure. Hybrid structure is the collective representation of all resonating structures and is most stable among all resonating structures. Resonating structures contribute to the stability of the molecule or compound.
- Hyperconjugation effect is also known as Nathan Baker effect and No bond resonance. It is a permanent effect. It is applicable on $$\sigma$$ bonded electrons, hence it is the delocalization of $$\sigma$$ electrons. It is applied for carbocation and free radical species. Hyperconjugation does not apply to carbanions. Hyperconjugation effect is also known as anchimeric effect.
Hence Inductive, Resonance and Hyperconjugation effect, all are permanent effects. On the other hand, the Electromeric effect is a temporary effect.

Thus, the correct option is A.

Note:
In inductive effect, electrons do not leave their original atomic orbital and only shift towards more electronegative elements. Inductive effect of hydrogen is taken to be zero. In resonance or mesomeric effect, resonating structures do not explain all the properties of ions or molecules but hybrid structures can explain all the properties of ions or molecules.