[thereforeiamx]

2,3-dibromobutane supposedly has two sets of enantiomers. one of the two sets of enantiomers has a mirror plane of symmetry. in the textbook, it says that this set are both of the same compound. is this possible? it doesn't really make sense to me. 

[Dan]

It sounds like the book is misleading.

There is one pair of enantiomers and one meso compound.

The point the book is probably making is that one "set of enantiomers" isn't actually a pair of enantiomers but they are the same compound, and is achiral since there is a plane of symmetry.

A molecule with a plane (or centre) of symmetry is achiral and therefore cannot be one of an enantiomeric pair.

[thereforeiamx]

that's weird hmmm. you would call this one pair of enantiomers and one pair of meso compounds diastereomers, correct?

how come the one pair of meso compounds aren't superimposable if they are the same compound then?

[Dan]

how come the one pair of meso compounds aren't superimposable if they are the same compound then?

They are superimposable. See pic.

There are 3 stereoisomers in total.