Question

Decreasing order of acidic strength order of following compound is

I > II > III

Answer 1

I > II > III

Answer 2

1. Cyclopentadiene (I):

It is acidic (pKa ≈ 16) because deprotonation produces the aromatic cyclopentadienyl anion.

2. Bicyclic compound (II):

It doesn’t form an aromatic anion upon deprotonation as effectively as (I), so it is less acidic.

3. Tricyclic compound (III):

Its structure does not favor aromatic stabilization upon deprotonation and is the least acidic.

Thus, the decreasing order of acid strength is:

$$\text{I} > \text{II} > \text{III}$$

Minimal Explanation:

Cyclopentadiene (I) is most acidic due to aromatic stabilization of its anion. Compound (II) is less acidic and compound (III) is the least acidic.