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Question #44305
The Question
Consider the following aromatic amines: (I) \ce{C6H5NH2} (II) \ce{2-CH3-C6H4NH2} (III) \ce{C6H5N(CH3)2} (IV) \ce{2-CH3-C6H4N(CH3)2}
Evaluate their basic strength in an aqueous medium at . Which of the following represents the correct decreasing order of their basicity ()?
Options
- A.
(IV) > (III) > (I) > (II)
- B.
(III) > (IV) > (I) > (II)
- C.
(II) > (I) > (IV) > (III)
- D.
(IV) > (II) > (III) > (I)
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Exception_Exposure
Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.
Concepts Behind This Question
Electronegativity Scales|Ortho-Effect in Anilines|Solvent Effects on Reactivity
Why This Question Is Tricky
Common Mistakes
Students often memorize the 'Ortho-Effect' as a blanket rule where ortho-substitution decreases basicity in anilines due to steric inhibition of solvation.
However, they fail to account for Steric Inhibition of Resonance (SIR) in N,N-dialkylanilines.
In primary anilines, the loss of solvation energy overpowers the effect, making 2-methylaniline less basic than aniline.
Conversely, in N,N-dimethylanilines, the bulky ortho-group forces the group out of the ring plane.
This breaks resonance, localizing electron density on the nitrogen atom and drastically increasing basicity, thus flipping the expected trend.
Additionally, students often incorrectly apply aliphatic amine solvation trends () to aromatic amines, forgetting that the bulky phenyl ring already dominates steric hindrance, allowing the effect of N-methyl groups to make tertiary anilines more basic than primary ones.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Classification of Elements and Periodicity in Properties - Class 11 Part 1 |
| Concept | Electronegativity Scales |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |