Question

Acetylene is treated with excess sodium in liquid ammonia. The product is reacted with excess of methyl iodine. The final product is

• A. But-1-yne
• B. but-2-yne
• C. but-1-ene
• D. but-2-ene

Answer 1

The correct option is B but-2-yne

Terminal alkynes are unusual for simple hydrocarbons in that they can be deprotonated using an appropriate base (typically $NaN{H}_2$ to generate a carbanion.
The acetylide carbanion is a good nucleophile and can undergo nucleophilic substitution reactions with $1^{o}or{2}^o$ alkyl halides to produce an internal alkyne.
$CH\equiv CH+NaN{H}_2⟶CH\equiv CNa\stackrel{NaN{H}_2}{⟶}NaC\equiv CNa\stackrel{C{H}_{3}I}{\to }C{H}_{3}C\equiv CC{H}_3\text{2-butyne}$