What is optical isomerism and how can you distinguish between optical isomers?

A molecule will exhibit optical isomerism if it contains a chiral centre/ an asymmetric carbon atom - in other words, if it contains a carbon atom with 4 different groups attached. Due to this property, these types of molecules have a mirror image that is non-superimposable upon itself. This means that you cannot map one molecule onto the other (unless you break some bonds!).

Due to the fact that these mirror images - or optical isomers - are quite similar, they often has similar chemical and physical properties, so cannot be distinguished by usual chemical or physical methods.

However, optical isomers have different effects on plane-polarised light (light that travels in a single plane). One isomer will rotate the plane of this plane-polarised light clockwise, and the other will rotate it anticlockwise. This is how you can distinguish the isomers from one another.