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Question #44342
The Question
Consider the base dissociation constants () of the following aromatic amines in aqueous solution at 298 K: \begin{enumerate} \item[(I)] \ce{C6H5NH2} \item[(II)] \ce{2,6-(CH3)2C6H3NH2} \item[(III)] \ce{C6H5N(CH3)2} \item[(IV)] \ce{2,6-(CH3)2C6H3N(CH3)2} \end{enumerate} Which of the following represents the correct decreasing order of basic strength?
Options
- A.
- B.
- C.
- D.
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
VSEPR Lone Pair Positioning|Ortho-Effect in Anilines
Why This Question Is Tricky
Common Mistakes
The question tests the critical boundary between the Ortho-effect (Steric Inhibition of Solvation) and Steric Inhibition of Resonance (SIR).
Students often apply a single rule universally—either assuming ortho-groups always decrease basicity due to steric hindrance (choosing C), or assuming they always increase basicity via +I/SIR (choosing B).
The 'Hidden Variable' is the size of the N-substituent: primary amines suffer the thermodynamic solvation penalty without SIR, while tertiary amines undergo SIR, which electronically supercharges the basicity enough to overcome the solvation penalty.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Chemical Bonding and Molecular Structure - Class 11 Part 1 |
| Concept | VSEPR Lone Pair Positioning |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |