Question

Is it not possible to have a diastereomer if there is only one chirality centre in a molecule?

Answer 1

It is possible for a structure to generate diastereomers without any chiral centres in the molecule. How?

Explanation:

By definition, diasereomers are geometric isomers that are not mirror images. Cis and trans isomers of olefins and rings fit these criteria, and are certainly geometric isomers. At least for olefins, for examples `"2-butylene"`, we can have the diatereomeric pair of cis and trans isomers. Their connectivity is the same; their geometry is manifestly different.