Question

Draw the alkynes formed when each dihalide is treated with excess base.

a.

b.

c.

d.

Short answer

The products formed after the treatment ${\text{NaNH}}_2$ is shown below:

Step-by-step solution

Type of the base used

${\text{NaNH}}_2$ is a strong base. When used in excess, it tends to abstract all the$\text{β}$ protons since, in these substrates, two leaving groups are present. As a result, the elimination product formed gives an alkyne.

Removal of β hydrogens

Removal of excess $\mathbf{\text{β}}$ hydrogens gives rise to the elimination product. Different types of $\text{β}$ hydrogens give different types of products. But here, different types of $\mathbf{\text{β}}$ hydrogens give a single product due to the formation of alkyne.

Representation of beta hydrogens

Formation of alkynes

Based on the steps, the products formed after the treatment with ${\text{NaNH}}_2$ s shown below:-

Representation of possible products in a

Representation of possible products in b

Representation of possible products in c

Representation of possible products in d