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Question #45090

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following carbocations generated as reactive intermediates in solvolysis reactions at $298\text{ K}$ : \begin{enumerate} \item[I.] Tricyclopropylmethyl cation ( $\ce{(c-C3H5)3C+}$ ) \item[II.] Tropylium cation ( $\ce{C7H7+}$ ) \item[III.] Triphenylmethyl cation ( $\ce{Ph3C+}$ ) \item[IV.] \textit{tert}-Butyl cation ( $\ce{(CH3)3C+}$ ) \end{enumerate} Identify the correct decreasing order of their thermodynamic stability.

Options

A.
II > I > III > IV
B.
III > II > I > IV
C.
II > III > I > IV
D.
II > III > IV > I

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

Reaction Intermediates Stability|Hyperconjugation Logic|Resonance Energy and Stability

Why This Question Is Tricky

Common Mistakes

This question targets the 'Cyclopropylcarbinyl Cation' paradox and the limitations of heuristic stability rules.

Students typically predict stability by counting resonance structures or hyperconjugative $\alpha$ -hydrogens, leading them to incorrectly assume the Triphenylmethyl cation (III) is more stable than the Tricyclopropylmethyl cation (I).

The 'Hidden Variable' is the superior orbital overlap of the Walsh orbitals (bent bonds) in the cyclopropylcarbinyl system compared to the sterically hindered, non-planar $\pi$ -system of the triphenylmethyl cation.

Recognizing aromaticity (Tropylium) as the dominant stabilizing factor completes the hierarchy.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	Reaction Intermediates Stability
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free