Question: Show how $\mathbf{HC}\mathbf{\equiv }\mathbf{CH}\mathbf{,}{\left({\mathrm{CH}}_3\right)}_{\mathbf{2}}{\mathbf{CHCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{Br}$can be used to prepare ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\mathbf{\equiv }{\mathbf{CCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{CH}{\left({\mathrm{CH}}_3\right)}_{\mathbf{2}}$ . Show all reagents, and use curved arrows to show movement of electron pairs.

The hydrogen attached to the terminal alkyne group of a compound can be easily abstracted by the attack of a strong base like .A general reaction is shown below:

Formation of acetylide anion

The acetylide ion formed can undergo ${\mathbf{S}}_{\mathbf{N}}\mathbf{2}$type attack at the electrophilic center of the alkyl halide.A general reaction is shown below:

S_N2 type reaction of acetylide with alkyl halide

The alkyne group present can first be subjected to proton abstraction, as shown below:

Attack of base

This nucleophile now reacts with one of the alkyl halides${\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{Br}$

The reaction is shown below:

Reaction of nucleophile with alkyl halide

The other hydrogen atom attached to the alkyne group is abstracted by similar mechanism.

Reaction of nucleophile with alkyl halide