How would you draw a six-carbon alkyne that can exist as a diastereomer?

A six carbon alkyne that can exist as a diastereomer is 1-ethynyl-2-methylcyclopropane.

One way for a compound to have is to have two chiral centres.

The only way we can do this with a six-carbon alkyne is to have a cyclopropane ring.

Then we can add an ethynyl and a methyl group to generate two chiral centres.

1-ethynyl-2-methylcyclopropane

Since there are two chiral centres and no plane of symmetry, there are ##2^2 = 4## stereoisomers.

Their structures are

Any isomer in one row is a diastereomer of the two isomers in the other row.

Isomers in the same row are a pair of .