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Question #43973
The Question
Consider the following substituted benzaldehydes subjected to Cannizzaro reaction conditions using at : (I) 4-Nitrobenzaldehyde (II) 3-Nitrobenzaldehyde (III) 2-Nitrobenzaldehyde (IV) 2,6-Dinitrobenzaldehyde
Which of the following represents the correct decreasing order of their initial reaction rates?
Options
- A.
I > II > III > IV
- B.
IV > III > I > II
- C.
IV > I > III > II
- D.
I > III > II > IV
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
Cannizzaro Mechanism|Inductive Effect Trends|Carboxylic Acid Strength
Why This Question Is Tricky
Common Mistakes
The problem tests the student's ability to distinguish between the electronic favorability of the first step (nucleophilic attack) and the kinetic requirements of the Rate Determining Step (hydride transfer).
Students who rely solely on electronic effects (-I, -M) will predict that ortho-substituted and di-ortho-substituted benzaldehydes react fastest due to increased electrophilicity (Option B).
The hidden variable is the severe steric hindrance in the bimolecular transition state of the hydride transfer.
Excessive ortho-substitution creates a steric bottleneck that destabilizes the transition state, completely reversing the rate trend predicted by simple inductive and mesomeric effects.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Aldehydes, Ketones, and Carboxylic Acids - Class 12 |
| Concept | Cannizzaro Mechanism |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |