Name: Mechanism of Addition Reactions of Alkenes
Uploaded: 2019-07-19
Duration: 11 min 16 s
Description: The most common reaction for an alkene is the addition reaction to a C=C double bond. Watch the video to learn more about the addition reactions of alkenes.

Question

Alkynes on reduction with sodium in liquid ammonia form trans alkenes. Will the butene thus formed on the reduction of

2

-butyne show the geometrical isomerism?

Accepted Answer

Alkynes undergo reduction to give alkenes and on further reduction they give alkanes. If the reaction is controlled, the reduction step can be stopped at alkenes. Alkyne when treated with $Na / liq . {NH}_{3}$ give trans alkenes which can show geometrical isomerism.

The reaction can be shown as follows:

Step 1: Formation of vinyl radical:

The cis-vinyl radical is less stable due to more electron repulsion on the same side of the bond. Thus, it converts into a trans form which is more stable due to staggering of electron and bonded pairs. Then formed trans-isomer of vinyl radical is attacked by the proton from ammonia.

Step 2: Double protonation of vinyl radical.

The negative charged developed on one carbon attacks the proton from ${NH}_{3}$ and another sodium atom loses its electron to develop a second negative charge on the atom. This negative charge is finally neutralised by attack of second proton to give a trans-but-2-ene. This but-2-ene produced shows geometrical isomers as cis and trans.

Alkynes on reduction with sodium in liquid ammonia form trans alkenes. Will the butene thus formed on the reduction of $2$ -butyne show the geometrical isomerism?

Important Questions on Hydrocarbons

Learn and Prepare for any exam you want !

Alkynes on reduction with sodium in liquid ammonia form trans alkenes. Will the butene thus formed on the reduction of 2-butyne show the geometrical isomerism?

Important Questions on Hydrocarbons

Learn and Prepare for any exam you want !

Alkynes on reduction with sodium in liquid ammonia form trans alkenes. Will the butene thus formed on the reduction of $2$ -butyne show the geometrical isomerism?