Question

Draw the structure of a dihalide that could be used to prepare each alkyne. There may be more than one possible dihalide.

a.

b.

c.

Short answer

The structure of a dihalide that could be used to prepare each alkyne are as follows:-

Step-by-step solution

Concentration of the base

The base used in these reactions where the dihalides get converted into an alkyne is taken in excess. Their high concentration allows them to be abstract more than one $\mathbf{\text{β}}$ proton. The base usually used is a strong base like sodium amide.

Position of β hydrogens and the leaving groups

The position of $\text{β}$ hydrogens and the leaving groups will be so that they allow the elimination reaction to take place to form an alkyne. The possible dihalides that form an alkyne are given below:

Representation of possible dihalide structures from a

Representation of possible dihalide structures from b

Representation of possible dihalide structures from c

Hence, the structure of a dihalide that could be used to prepare each alkyne are as follows:-

Formation of dihalide structures from a

Formation of dihalide structures from b

Formation of dihalide structures from c