Opening image: Ball-and-stick model of β-D-glucose. The six-membered glucopyranose ring lies in the plane of the screen; for clarity the hydrogen atoms of the equatorial ring substituents have been omitted, but you can them back into the model here.
In the β anomer all five hydrogen atoms attached to the ring carbons are axial. Since the symmetry axis of the molecule is perpendicular to the screen, you are looking down two axial bonds. Rock the molecule up and down to see the other three axial bonds.
the molecule 180° brings the other three axial bonds into view, but only as white dots. For a better view of the axial bonds, the molecule so that its axis is in the plane of the screen.
Now from the traditional "ball representation" for the axial hydrogens to the actual van der Waals radius for hydrogen.
The relatively bulky –OH and –CH2OH groups are equatorial in the β anomer of D-glucose.
between spacefilled and ball-and-stick models of β-D-glucose.
Steric crowding between axial substituents becomes a problem unless all the axial groups are hydrogens. This is especially apparent if you the molecule along its symmetry axis. the molecule 180°.
α-D-glucose. Recall that the anomeric carbon is easily identified as the only carbon bonded to two oxygen atoms. The α anomer has the anomeric –OH group down, or axial.
Stick model of α-D-glucose is shown in JSmol; for clarity only the ring hydrogen atoms are shown. the anomeric carbon (C1).
The anomeric carbon is now shown in magenta.
One should realize that glucose is not a static molecule. Thermal motions include vibrations leading to random fluctuations in bond angles and distances. JSmol can show computer simulations of this thermal motion.
animation on and off.
between spacefill and ball-and-stick models. Notice the frequent collisions between the axial anomeric hydroxyl group and the axial hydrogens. Now you know why the β anomer is more stable than the α anomer.