In this article I review one of the most significant accomplishments of Frank H. Westheimer, one of the most respected chemists of the 20th century. This accomplishment was a series of stereospecific enzymatic oxidation and reduction experiments that led chemists to recognize what we now call the enantiotopic and diastereotopic relationships of atoms, or groups of atoms, within molecules. Each experiment provides an example that can be used in the teaching of introductory organic chemistry. (Contains 1 figure and 3 notes.)