Question

${CH}_{3}C\equiv C{CH}_3\underset{}{\overset{H_2/Pt}{\to }}A\underset{}{\overset{D_2/Pt}{\to }}B$

The compounds $A$ and $B$ respectively are:

• A. cis-butene-2 and rac-2,3-dideuterobutane
• B. trans-butene-2and rac-2,3 dideuterobutane
• C. cis-butene-2 and meso-2,3-dideuterobutane
• D. trans-butene-2 and meso-2,3-dideuterobutane

Answer 1

The correct option is C cis-butene-2 and meso-2,3-dideuterobutane

The compounds $A$ and $B$ are cis-butene-2 and meso-2,3-dideuterobutane respectively.

${CH}_{3}C\equiv C{CH}_3\underset{}{\overset{H_2/Pt}{\to }}\underset{\text{A}}{{CH}_3\stackrel{\stackrel{\text{H}}{|}}{C}=\stackrel{\stackrel{\text{H}}{|}}{C}{CH}_3}\underset{}{\overset{D_2/Pt}{\to }}\underset{\text{B}}{{CH}_3\stackrel{\stackrel{\text{D}}{|}}{\underset{\underset{\text{H}}{|}}{C}}-\stackrel{\stackrel{\text{D}}{|}}{\underset{\underset{\text{H}}{|}}{C}}{CH}_3}$
Catalytic hydrogenation of alkynes gives cis-alkene which in turn adds deuterium atoms in presence of $Pt$ again in cis-manner forming meso-2,3-dideuterobutane. The net reaction is the conversion of $C\equiv C$ to $C-C$ single bond and addition of a molecule of $H_2$ and a molecule of $D_2$.