The Question is from neet-chemistry organic-chemistry-basics , and it was created by the author Mr. S M HUSSAIN

Question

Which of the following statements is INCORRECT regarding the mesomeric effect?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
	**Primary Concept**: Mesomeric Effect (Resonance Effect)
	**Related Topics**: Conjugation, Resonance Structures, Electron Delocalization, Inductive Effect
	**Prerequisites**: Understanding of chemical bonding, Lewis structures, and electron distribution in molecules.
## SOLUTION PATHWAY
**Given Information**:
	We are analyzing the properties of the mesomeric effect.
**Method & Steps**:
	1. **Define Mesomeric Effect**: The mesomeric effect is a permanent effect that describes the delocalization of electrons (pi electrons or lone pairs) in conjugated systems. 
		Reasoning: Conjugation allows electrons to be shared over multiple atoms, leading to increased stability.
	2. **Types of Mesomeric Effect**: It can be positive (+M/+R) when a group donates electrons into the conjugated system or negative (-M/-R) when a group withdraws electrons from the conjugated system.
		Working: Examples include -OH, -NH2 (+M) and -NO2, -CN (-M) groups. 
	3. **Comparison with Inductive Effect**: Unlike the inductive effect, which is a distance-dependent polarization of sigma bonds, the mesomeric effect involves the delocalization of pi electrons and is transmitted throughout the conjugated system.
		Result: The mesomeric effect is a permanent effect due to the inherent nature of electron delocalization within conjugated systems.
		Verification: The incorrect statement is 'It is a temporary effect'.
## OPTION ANALYSIS
[A] ✓: It involves the delocalization of π electrons or lone pairs. This is a correct description of the mesomeric effect as it involves the movement of pi electrons or lone pairs within a conjugated system.
[B] ✓: It operates only in conjugated systems.  The mesomeric effect requires a conjugated system for the delocalization of electrons to occur. This is a correct statement.
[C] ✓: It can be positive (+M/+R) or negative (-M/-R). This is correct as the mesomeric effect can be electron-donating (+M) or electron-withdrawing (-M) depending on the substituent.
[D] :x: It is a temporary effect. This is incorrect. The mesomeric effect is a permanent effect, resulting from the resonance within the molecule. It's the resonance structures that represent different electron distributions, but the actual molecule exists as a hybrid of these structures, making the delocalization permanent.
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing Mesomeric and Inductive Effects: The inductive effect is through sigma bonds and is distance-dependent, while the mesomeric effect is through pi electrons in a conjugated system.
			How to avoid: Remember that mesomeric effect requires conjugation and involves pi electrons or lone pairs.
		2. Considering Mesomeric Effect Temporary: The resonance structures might give the impression of temporary shifts, but the actual molecule exists as a resonance hybrid with permanent delocalization.
			How to avoid: Remember that the molecule is a hybrid of resonance structures, making the mesomeric effect permanent.
	**Quick Tips**:
		1. Look for conjugated systems (alternating single and double/triple bonds) to identify the possibility of mesomeric effect.
		2. Remember 'M' for Mesomeric and 'movement' of electrons.

Mr. S M HUSSAIN · Answer

It involves the delocalization of π electrons or lone pairs

Mr. S M HUSSAIN · Answer

It operates only in conjugated systems

Mr. S M HUSSAIN · Answer

It can be positive (+M/+R) or negative (-M/-R)

Mr. S M HUSSAIN · Answer

The correct Option is "It is a temporary effect"

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