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Unformatted text preview: Chem 057 CENTER FOR LEARNING AND TEACHING Handout #8 J. Walcott LEARNING STRATEGIES CENTER Fall 2007 Review Guide #5 Lectures: 9/17/07 9/21/07 Chapter 5 Principles of Stereochemistry I. Chirality A. A molecule is said to be chiral when it is not congruent or superimposable on its mirror image. A molecule which is superimposable on its mirror image is said to be achiral . A molecule that has an internal plane of symmetry is achiral. Enantiomers are stereoisomers that have a non- superimposable mirror image relationship and are thereby chiral molecules. Enantiomers are identical in all physical properties (e.g. density, melting point, boiling point, etc.) except for the way in which they interact with plane polarized light. Enantiomers also have identical chemical properties in an achiral environment (i.e. typical laboratory conditions). B. A stereocenter is a carbon atom with 4 different groups attached to it. (Note: A stereocenter as we have defined it, is the same as an asymmetric carbon as defined in the text.) The presence of a single stereocenter (asymmetric carbon atom) guarantees chirality. A molecule is usually not chiral if there are no stereocenters. If there is more than one stereocenter it may or may not be chiral. The way to check the chirality is to see if the molecule is superimposable or congruent on...
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