Question

When a tertiary alcohol ‘A’ (C₄H₁₀O₄) reacts with 20% H₃PO₄ at 358 K, it gives a compound ‘B’ (C₄H₈) as a major product. The IUPAC name of the compound ‘B’ is :

• A. But-1-ene
• B. But-2-ene
• C. Cyclobutane
• D. 2-Methylpropene

Answer 1

The Correct Option is D

• Tertiary Alcohol 'A' (C₄H₁₀O): A tertiary alcohol undergoes dehydration (loss of water) when treated with a strong acid like phosphoric acid (H₃PO₄) at high temperature (358 K).
• The dehydration reaction typically leads to the formation of an alkene.
• Since the alcohol is tertiary, it undergoes a rearrangement to form the most stable carbocation intermediate, and the major product will be formed by the elimination of water in such a way that the most stable, substituted alkene is produced.
• 'B' (C₄H₈): This compound is a 4-carbon alkene formed by the dehydration of the tertiary alcohol. The possible products could be but-2-ene or 2-methylpropene (also known as isobutene).
• 2-Methylpropene is the major product because the tertiary carbocation intermediate formed during dehydration can undergo a shift to create the more stable alkene, 2-methylpropene.

Thus, the IUPAC name of the compound 'B' is 2-Methylpropene, making option (D) the correct answer.