Question

Compound (X) [Phenylacetylene] is subjected to the sequence of reactions:

Molar mass of the major product (Y) formed is _______ \(g \cdot mol^{-1}\). (Given molar mass in \(g \cdot mol^{-1}\) C:12, H: 1, O: 16)

• A. 90
• B. 118
• C. 160
• D. 125

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The sequence involves bromination, elimination to form an alkyne, alkylation of the terminal alkyne, and finally a stereoselective Birch reduction.

Step 2: Key Formula or Approach:
1. \(Ph-C\equiv CH \xrightarrow{Br_2} Ph-CBr=CHBr\)
2. \(Ph-CBr=CHBr \xrightarrow{NaNH_2 \text{ (excess)}} Ph-C\equiv C^- Na^+\)
3. \(Ph-C\equiv C^- Na^+ \xrightarrow{CH_3I} Ph-C\equiv C-CH_3\) (1-phenylpropyne)
4. \(Ph-C\equiv C-CH_3 \xrightarrow{Na/NH_3} \text{trans-1-phenylpropene}\).

Step 3: Detailed Explanation:
The final product (Y) is trans-1-phenylpropene.
Chemical Formula: \(C_9H_{10}\)
Calculation of Molar Mass:
\(9 \times 12 (\text{for C}) + 10 \times 1 (\text{for H}) = 108 + 10 = 118 \text{ g/mol}\).

Step 4: Final Answer:
The molar mass of the product (Y) is 118 \(g \cdot mol^{-1}\).