Question

How do you draw propyne?

Answer 1

`H_3C-C-=CH`.

Explanation:

The molecular formula of propyne, `C_3H_4`, specifies 2 degrees of unsaturation; two double bonds as required.

Answer 2

• Looking at the prefix, "prop" means three, so you have three carbons.
• Looking at the suffix, "yne" means it's an alkyne, so you have at least one triple bond. The general formula for a straight-chained alkyne is `C_nH_(2n-2)`, so you should get `C_3H_4`.
• There is nothing else in the name, so there is only one triple bond.

Therefore, you have three carbons connected, and two of them are bonded via one triple bond. Fill in the 4 hydrogens by knowing the valency of carbon as `4`.

This would be propyne.

Had you drawn:

`"H"_2"C"="C"="CH"_2`

That would be allene, which is incorrect. There are not two double bonds. It's an alkyne, not an alkene.