Imagine two objects or molecules at first glance corresponding in all characteristics. However, they are not identical and they are clearly distinguishable.While this seems confusing, it is a common problem in chemistry that two compounds show identical empirical formulas, densities, refraction indices, boiling and freezing points, and spectra but totally different pharmaceutical effects! What is the difference? One is confronted with the same type of difference putting on his shoes or gloves. The left glove does not fit the right hand. The left and right hand are not superimposable even though they have a mirror-image relationship.
- Objects or molecules which cannot be superimposed with their mirror image are called chiral. If they are superimposable with their mirror image, they are called achiral.