Question

Which of the following reagents should be used to convert to Question 2 options: A) Na, NH3 B) H2, Pt C) H2, Lindlar's catalyst D) HgSO4, H2O

Answer 1

A

Step-by-step explanation:

If we intend to achieve the anti addition of Hex-3-yne to yield (E) Hex-3-ene, the we must use Na/NH3. The first step of the reaction involves the transfer of an electron from sodium to the alkene; this yields a radical anion. Strong electron replusion ensues between the single electron and the lone pair on the carbon. This now forces the both to be found at a trans position to each other and this is the basis of the stereochemistry of the product.

Secondly, the radical anion abstracts a proton from ammonia. Another sodium atom transfers an electron leading to the formation of a vinyl carbanion, the alkyl groups are now trans to each other.

This carbanion now abstracts a proton from ammonia and the final product is formed.