Question

Please Someone?

Answer 1

A diastereomer is a non-superimposable non-mirror image of a molecule with more than one chirality center.

A simple heuristic I use is: Look for molecules that have at least one chirality center in common and one or more inverted.

I find the method with the highest certainty is using RS configuration. I've noted each's configuration below (the more practice you get, the quicker you will get).

Hence,

`(iii)` and `(iv)` are the same molecule, as well as enantiomers of `(i)`.

`(i)` and `(ii)` are diastereomers. `(1)`