Bluffton University

Organic Chemistry

Molecular Models:
Chiral centers
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When both chiral centers in a molecule have the same substituents, the molecule as a whole may or may not be chiral. In general, if one half of a molecule is the mirror image of the other half, the molecule contains a plane of symmetry and cannot be chiral even though it may contain chiral centers.

Consider 2,3-dibromobutane. Like 3-bromo-2-butanol it has two chiral centers and therefore four (22) possible configurations: RR, SS, RS and SR. However, if you examine the four molecules below you will see that one pair is identical! Molecules which contain chiral centers but are not themselves chiral are called meso, and we refer to them as (for example) meso-2,3-dibromobutane.

2,3-dibromobutane 2,3-dibromobutane
2,3-dibromobutane 2,3-dibromobutane
Assign R or S configuration to each of the chiral centers in the molecules shown above. Which molecules contain a plane of symmetry?
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Copyright © 1998, 1999, 2000, 2003, 2007 by Daniel J. Berger. This work may be copied without limit if its use is to be for non-profit educational purposes. Such copies may be by any method, present or future. The author requests only that this statement accompany all such copies. All rights to publication for profit are retained by the author.