Overview of Stereochemistry
Stereochemistry is the branch of chemistry concerned with the spatial arrangements of atoms in molecules. Stereoisomers are molecules which do not differ in the sequential arrangement of atoms, but the spatial arrangment. In our earlier chapter, the Conformations of Organic Molecules, we were concerned with one sub-class of stereoisomerism, conformational isomerism, in which interconversion between the differing forms may occur without breaking bonds. In contrast, however, configurational isomers, the other type of stereoisomers, may not be interconverted without breaking bonds. If two configurational isomers are mirror images, they are enantiomers. Configurational isomers which are not mirror images are enantiomers.
Stereochemistry on the MCATStereochemistry is a crucial topic for the MCAT. Nearly every exam will contain at least one question dealing directly with stereochemistry and several questions dealing indirectly. An MCAT passage presenting a reaction mechanism will likely be followed by at least one question dealing with issues such as inversion of configuration or racemization. Students are often required to recognize meso- forms on the MCAT or predict the number of stereoisomers a structure may have. Watch for stereochemistry to be presented on the MCAT in an unusual context such coordination chemistry.