The Fischer Projection
Rules for Handling Fischer Projections - Rule 2
- Rule 2
- In a Fischer projection any three of the substituents of an asymmetric carbon may be rotated clockwise or counterclockwise, while the fourth is arrested in its position.
Such a rotation is equivalent to an internal bond rotation on the bond axis between the arrested fourth substituent and the asymmetric carbon (run the animation of this internal bond rotation). Therefore, it is an alteration of the conformation and not of the configuration. The resulting Fischer projection represents the same enantiomer as the initial Fischer projection.
An exercise with answer for the application of the Fischer projection rules:
Ascertain whether the following three Fischer projections depict identic or opposite enantiomers.