Question

But-2-yne and hydrogen (one mole each) are separately treated with (i) Pd/C and (ii) Na/liq.NH₃ to give the products X and Y respectively.

Identify the incorrect statements.
A. X and Y are stereoisomers.
B. Dipole moment of X is zero.
C. Boiling point of X is higher than Y.
D. X and Y react with O₃/Zn + H₂O to give different products.
Choose the correct answer from the options given below :

• A. A and B Only
• B. A and C Only
• C. B and C Only
• D. B and D Only

Hint:

To remember: "Cis" starts with C, like "Pd/C" (though usually poisoned). "Trans" involves "Sodium" ($Na$). Symmetrical alkenes always give the same carbonyl products in ozonolysis regardless of geometry.

Answer 1

The Correct Option is D

The question involves the hydrogenation of but-2-yne using two different sets of reagents to produce compounds X and Y:

Let's analyze each part:

1. Reaction with Pd/C:

   Using palladium on carbon (Pd/C) with hydrogen fully hydrogenates the alkyne to an alkane. Therefore, but-2-yne will be converted to butane (X).

2. Reaction with Na/Liq.NH₃:

   In the presence of sodium in liquid ammonia (Birch reduction), the alkyne is converted to a trans-alkene. Therefore, but-2-yne is converted to trans-but-2-ene (Y).

3. Analysis of the Statements:

   • A. X and Y are stereoisomers: Incorrect. X is butane (an alkane) and Y is trans-but-2-ene (an alkene). They are not stereoisomers.
   • B. Dipole moment of X is zero: Correct. Since butane is symmetrical, it has no dipole moment.
   • C. Boiling point of X is higher than Y: Correct. The boiling point of alkanes (butane) is higher than that of alkenes (trans-but-2-ene) due to stronger van der Waals forces.
   • D. X and Y react with O₃/Zn + H₂O to give different products: Incorrect. Butane will not react with ozonolysis, while trans-but-2-ene will give acetaldehyde.

Conclusion: The incorrect statements are B and D. Therefore, the correct answer is:

B and D Only