Question

Which amongst the following be most readily dehydrated under acidic conditions?

• A.
• B.
• C.
• D.

Answer 1

The Correct Option is C

Because of the existence of conjugation in the resulting product the correct answer is option (C):

Correct Answer: Option 3

This question tests your understanding of the acid-catalyzed dehydration of alcohols, a key concept in organic chemistry. Dehydration of alcohols typically proceeds via an E1 (unimolecular elimination) mechanism under acidic conditions, especially when the formation of a stable carbocation intermediate is possible.

Let’s examine the core principle: In acidic medium, an alcohol loses water to form a carbocation, and the ease of dehydration depends largely on the stability of the resulting carbocation. More stable carbocations (like tertiary > secondary > primary) favor faster dehydration.

Option 1: This compound contains a nitro group (NO₂) at the β-position. The OH group is on a secondary carbon, but the adjacent nitro group is electron-withdrawing, which destabilizes the carbocation intermediate. Hence, this compound will not dehydrate readily.

Option 2: Similar to option 1, it contains a nitro group adjacent to the OH-bearing carbon. Although the carbon is more substituted (potential for tertiary carbocation), the strong electron-withdrawing nature of NO₂ again reduces carbocation stability.

Option 3: This is the correct option. It contains a tertiary alcohol group (the OH is bonded to a carbon that is itself bonded to three other carbon atoms). Upon dehydration under acidic conditions, this compound will form a highly stable tertiary carbocation, which greatly facilitates the elimination of water and formation of an alkene. Tertiary carbocations are significantly more stable than secondary or primary ones due to hyperconjugation and inductive effects.

Option 4: This compound also has a nitro group, and the OH groups are on less substituted carbons. The presence of NO₂ again destabilizes the intermediate, and the molecule lacks the structural environment for tertiary carbocation stabilization.

Conclusion: Among all the choices, Option 3 forms a stable tertiary carbocation upon dehydration, making it the compound that will be most readily dehydrated under acidic conditions. Understanding the role of carbocation stability and electron-donating or withdrawing groups is essential for mastering elimination reactions and reaction mechanisms in organic chemistry