91Ó°ÊÓ

Acetylide ions are formed as a result of proton abstraction from an acetylene group.The anion hence formed can be used as a reagent for nucleophilic substitution.

The reactions are shown below:

a.

Reaction a.

b.

Reaction b.

c.

In this case, the electrophilic carbon center is a $3°$carbocation, and thus does not favor attack. Instead, elimination occurs.

Reaction c.

d.

The carbon centers are equivalent, thus the attack can take place from any of the two sides.

Reaction d

e.

Favoring localid="1648805732814" ${\mathrm{S}}_{\mathrm{N}}2$attack, the ion would tend to attack at the less substituted carbon center.

Reaction e