Projection Formulas

The sawhorse or Newman representations of 2-butanol, 5a and 5b and 6a and 6b, are excellent for showing the arrangements of the atoms in conformations, but are needlessly complex for representing the stereochemical configuration. Fischer projection formulas are widely used to show configurations and are quite straightforward, once one gets the idea of what they represent..

Figure 5-11: Front and side views of planar molecules showing some conventions used to indicate perspective

The projection formulas of 2-butanol are 5c and 6c:

Figure 5-12.

Figure 5-12: Procedure for relating a projection formula to a configurational drawing with the aid of a ball-and-stick model. Assemble the ball-and-stick model over the projection formula (here 5c) so that the groups are arranged by the convention of the formula (horizontal bonds out, vertical bonds back), then turn the model so the appropriate groups, here CH3 and H, are parallel to the plane of the paper and make the perspective drawing agree with the model. The reverse procedure translates the perspective drawing into the projection formula.