Optical Isomerism

The challenge was to make an isomer of butanol which had two possible structures, yet both had the same structural formula:

These are called enantiomers or optical isomers. They are very interesting compounds and important in nature. However, the only physical property that can be used to tell them apart is their ability to rotate plane-polarised light - one isomer rotates it clockwise, while the other rotates it anti-clockwise.