Fischer Projection Structures
I. A Single Stereocenter
q Fischer structures can be used to simply represent absolute configurations of chiral compounds at their stereocenters. An advantage of such structures is that they can easily represent multiple stereocenters, and allow easy identification of planes of symmetry, etc.
q The Fischer structures of (R)-2-butanol and its enantiomer are shown below.
q You are not expected to be able to see from a given Fischer structure whether the configuration is R or S, but if given the structure of R you should be able to draw the Fischer structure of its enantiomer.
II. Two Equivalent Stereocenters.
q Given a Fischer structure of a molecule having two stereocenters, you should be able to draw the Fischer structure of its enantiomer and the other stereoisomers.
q Given the configuration of the the original stereoisomer, you should be able to designate the stereochemistry of all of the other stereoisomers.
q Note that the Fischer structure implies an eclipsed conformation.
q Consider 2,3-dibromobutane:
q So, if given the Fischer structure of say the S,S stereoisomer, you should be able to draw the structure of its enantiomer and any other stereoisomers.
III. Two Non-equivalent Stereocenters.
q Consider 3-chloro-2-butanol:
q Again, given one structure and its designation, you should be able to draw and designate all other stereoisomers. Of course, reflection in the mirror reverses all configurations. Also, interchanging any two groups inverts the configuration.