Draw the structure of the starting material needed to make 2-methylhept-3-yne using sodium amide in liquid ammonia

3,4-dibromo 2-methylheptane

Explanation:

Alkynes can be synthesized by using sodium amide in liquid ammonia, when the starting material is a vicinal dibromoalkane. This means an alkane in which there's a Br group in two carbons next to one another.

In the attached picture you can see the reaction.

see picture

Explanation:

Although the previous answer may be correct, the question is incomplete, the completed question is:

Draw the structure of the starting material needed to make 2-methylhept-3-yne using sodium amide in liquid ammonia followed by 1-bromopropane.

Now, the previous answer is also incorrect, because the starting material with the two bromine in carbon 3 and 4, the first reaction taking place is the substracting of the hydrogen from carbon 5, and not carbon 3 because it's bulkier than carbon 5. So the majority product formed will be a double bonded product and not a triple bond. Therefore, this answer is incorrect.

Now, that we have completed the question the Starting material would have to be the following:

CH3 - CH(CH3) - C ≡ CH

When this reactant, is in presence of NaNH2, the NH2 substract the Hydrogen from carbon 1, and then, this will attack as nucleophyle to the carbon 1 of the bromopropane and formed the desired product.

The mechanism is as following in the picture.