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Question #44029
The Question
Consider the following substituted anilines: (I) \ce{p-Fluoroaniline} (II) \ce{p-Chloroaniline} (III) \ce{2,4,6-Trinitroaniline} (IV) \ce{N,N-Dimethyl-2,4,6-trinitroaniline}
Which of the following represents the correct decreasing order of their basic strength in aqueous medium at ?
Options
- A.
(I) > (II) > (IV) > (III)
- B.
(II) > (I) > (III) > (IV)
- C.
(I) > (II) > (III) > (IV)
- D.
(II) > (I) > (IV) > (III)
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Mechanism_Trap
Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.
Concepts Behind This Question
Basicity-Solvation Competition|Aniline Resonance Pitfalls|Electrophilic Substitution Control
Why This Question Is Tricky
Common Mistakes
This problem tests two major exceptions in the basicity of substituted anilines.
First, the competition between and effects in halogens: students often assume p-fluoroaniline is the weakest base due to fluorine's maximum electronegativity ().
However, F's strong effect compensates for its , making it more basic than p-chloroaniline.
Second, the Steric Inhibition of Resonance (SIR) effect: students assume N,N-dimethyl-2,4,6-trinitroaniline is less basic than 2,4,6-trinitroaniline due to increased steric hindrance to solvation.
However, the bulky \ce{-NMe2} group is forced out of plane, preventing lone pair delocalization ( of nitro groups is nullified).
This localized lone pair makes it significantly more basic than the planar 2,4,6-trinitroaniline.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Amines - Class 12 |
| Concept | Basicity-Solvation Competition |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |