In the given reactions identify A and B [figure] CH3-C C-CH3 + H2 Na/Liquid NH3 “B”
- A : n-Pentane B : Cis - 2 - butene
- A : 2-Pentyne B : Cis-2-butene
- A : n-Pentane B : trans-2-butene
- A : 2-Pentyne B : trans-2-butene
Answer
(4) A : 2-Pentyne B : trans-2-butene
Solution
Reaction 1: H2 on the catalyst surface adds syn (both H on the same side) ⇒ alkyne → cis-alkene
∵ product is cis-2-pentene ⇒ A = CH3-C C-C2H5 (2-pentyne); an alkane (n-pentane) cannot take up H2
Reaction 2: Na/liquid NH3 (Birch reduction) adds the two H anti ⇒ trans-alkene
[figure]
Answer: (4)