How do you draw a diastereomer?

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Answer 1 · 2016-09-01T01:15:28

You change the configuration of one of the chiral centres.

Diastereomers are stereoisomers that are not superimposable and are not mirror images of each other.

A compound must have at least two chiral centres to have diastereomers.

Let's look at a Compound $A$ $"A"$ with two chiral centres.

$C2$ $"C2"$ and $C3$ $"C3"$ are chiral centres.

If we change the configuration at $C2$ $"C2"$ , we get Compound $B$ $"B"$ .

This is not a mirror image of $A$ $"A"$ , nor is it superimposable with $A$ $"A"$ . It is a diastereomer of $A$ $"A"$ .

Now, let's change the configuration of just $C3$ $"C3"$ to get Compound $C$ $"C"$ .

This is also a diastereomer of $A$ $"A"$ .

BUT, if we change the configuration of both carbon atoms, we get Compound $D$ $"D"$ .

This is nonsuperimposable on $A$ $"A"$ .

However, it is a mirror image of $A$ $"A"$ , because both $OH$ $"OH"$ groups are on dashes instead of on wedges.

$A$ $"A"$ and $D$ $"D"$ are enantiomers.