Before You Begin
Question #43975
The Question
Consider the electrophilic monochlorination of two isomeric tertiary amines, \textbf{X} (4-methyl--dimethylaniline) and \textbf{Y} (2-methyl--dimethylaniline), using \ce{Cl2} in glacial acetic acid at 298 K in the dark. Let and be the major monochlorinated products of \textbf{X} and \textbf{Y}, respectively. Which of the following correctly identifies and ?
Options
- A.
2-chloro-4-methyl--dimethylaniline; 5-chloro-2-methyl--dimethylaniline
- B.
2-chloro-4-methyl--dimethylaniline; 4-chloro-2-methyl--dimethylaniline
- C.
3-chloro-4-methyl--dimethylaniline; 5-chloro-2-methyl--dimethylaniline
- D.
3-chloro-4-methyl--dimethylaniline; 4-chloro-2-methyl--dimethylaniline
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
DDT and Freon Chemistry|Ortho-Effect in Anilines|Electrophilic Substitution Control
Why This Question Is Tricky
Common Mistakes
The question tests the 'Steric Inhibition of Resonance' (SIR) or 'Ortho-Effect' in substituted anilines.
Students typically rely on a rigid hierarchy of activating groups, assuming the strongly activating group will always dominate over and direct ortho/para to itself.
However, in 2-methyl--dimethylaniline, steric clash forces the group out of planarity, nullifying its effect.
The hidden variable is this conformational change, which shifts the directing power from the nitrogen substituent to the weaker, but planar, methyl group, drastically altering the regioselectivity of the electrophilic aromatic substitution.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Haloalkanes and Haloarenes - Class 12 |
| Concept | DDT and Freon Chemistry |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |