Question

Choose the correct statements(s) regarding the following reaction:
$Alkyne\stackrel{X}{\to }R-CH=CH-R$

• A. If $X$ is $Na$ in liquid ${NH}_3$, then product will have trans configuration
• B. This reaction is an example of controlled hydrogenation
• C. $X$ may be $H_2$ with $Ni$ or $Pd$ or $Pt$
• D. If $X$ is Lindlar's catalyst, then the product will have cis configuration

Answer 1

Answer: (A), (B), (D)

The correct options are
A If $X$ is $Na$ in liquid ${NH}_3$, then product will have trans configuration
B This reaction is an example of controlled hydrogenation
D If $X$ is Lindlar's catalyst, then the product will have cis configuration

1. Option A is correct. The partial reduction of alkynes involves sodium (Na) and ammonia (${NH}_3$). This ends up reducing the alkyne to give the trans alkene.
2. Option B is correct. This reaction is a controlled hydrogenation as the degree of hydrogenation is controlled by restricting the amount of hydrogen/alky group, reaction temperature and time, and the catalyst
3. Option C is wrong as alkyne is converted to alkanes by adding Pd/Ni/Pt and it is not a controlled hydrogenation case.
4. Option D is correct. With Lindlar's catalyst, the cis configuration is obtained.