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An unknown alkyne A having the molecular formula C ₆ H ₁₀ reacts with H ₂ in the presence of Lindlar's catalyst to give an alkene B . Reductive ozonolysis of B (using O ₃ followed by Zn / H ₂ O ) yields only propanal. When the same alkyne A is treated with sodium in liquid ammonia, it gives an alkene C . Identify the correct statement comparing the physical properties of isomers B and C .

Options

  1. AB has zero dipole moment and a higher melting point than C
  2. BB has a non-zero dipole moment and a higher melting point than C
  3. CC has zero dipole moment and a higher melting point than B
  4. DC has a higher dipole moment and a lower melting point than B

Correct answer

C. C has zero dipole moment and a higher melting point than B

Step-by-step solution

Reductive ozonolysis of B yields only propanal ( CH ₃ CH ₂ CHO ). This indicates that B is a symmetrical alkene, specifically hex- 3 -ene. Thus, the starting alkyne A is hex- 3 -yne. Reaction of hex- 3 -yne with H ₂ and Lindlar's catalyst yields the cis-isomer. Therefore, B is cis-hex- 3 -ene. Reaction of hex- 3 -yne with Na in liquid NH ₃ yields the trans-isomer. Therefore, C is trans-hex- 3 -ene. The trans-isomer ( C ) is symmetrical and its individual bond dipoles cancel out, resulting in a zero dipole moment. I

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