Integrated SequencePhysics Chemistry Organic Biology

Web Resources

Virtual Textbook of Organic Chemistry - General Summary of Isomerism and Molecular Descriptors
Nice set of figures to help organize the different types of isomerism.

University of Calgary - Stereochemistry
Definition of the main types of isomers.



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Special points of emphasis

Abnormal Psychology

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 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. There is not uniformity of agreement on the definition of enantiomers, however. Some authors include cis - trans isomers as enantiomers, while other others only include forms differing at chiral centers that are not mirror images (having multiple chiral centers).

Stereochemistry 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 often be followed by at least one question dealing with issues such as inversion of configuration or racemization. Students are often asked 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 as coordination chemistry.




Stereochemistry

Coordination Chemistry

First semester organic chemistry typically provides undergraduates their most thorough treatment of the topics of geometrical and optical isomerism, but organic chemistry is not the only context for these types of isomerism. Geometrical and optical isomerism are also important in coordination chemistry, the study of compounds formed between metal ions and neutral or negatively charged molecules to form a metal complex.

In other words, a coordination complex consists of a metal ion bonded to one or more groups of molecules, which, when bonded, are called its ligands. As with organic compounds, coordination complexes with different geometic arrangements of ligands are called geometric isomers whereas isomers whose structures are mirror images of each other are called optical isomers. It would be typical of the MCAT to ask a question about optical isomers but in the context of coordination chemistry to see if you can apply what you already know in a new context.








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