D-Glucose is an aldohexose with four chiral carbons. In Panel 2 the conformation of glucose is such that the vertical bonds of the chiral carbon are projecting into the plane of the screen (Carbon chain circles around, so that carbon #1 (blue halo) meets carbon #6 (yellow halo).) and the horizontal bonds are projecting out of the plane of the screen. Imagine taking hold of carbon #1 (double bonded to oxygen and has blue halo), and pulling it to the top of the screen without rotating any bonds and then projecting the structure on to a 2D surface. The projected structure (Fischer Projection) will have the same configurations about carbons 2 (magenta halo), 3 (orange halo), 4 (red halo) and 5 (green halo) as that of the structure of Panel 1. The configuration of the bottom most chiral carbon (carbon #5) of the Fischer project is used to determine the D/L assignment. The structure in Panel 1 has the hydroxyl group on the right making it the D enantiomer. Compare the orientations of the hydroxyl groups in Panel 1 to those in the structure (saw-tooth conformation) of Panel 3. This comparison shows that the normally used saw-tooth conformation can not be used to make the enantiomeric assignment.