Editing Monosaccharide (section)

===Configuration of monosaccharides===
Like many chiral molecules, the two stereoisomers of glyceraldehyde will gradually rotate the [[Optical rotation|polarization direction]] of linearly [[polarized light]] as it passes through it, even in solution.  The two stereoisomers are identified with the prefixes {{sc|D}}- and {{sc|L}}-, according to the sense of rotation: {{sc|D}}-glyceraldehyde is [[dextrorotatory]] (rotates the polarization axis clockwise), while {{sc|L}}-glyceraldehyde is [[levorotatory]] (rotates it counterclockwise).

[[File:DL-Glucose.svg|right|thumb|300px|{{sc|D}}- and {{sc|L}}-glucose]]
The {{sc|D}}- and {{sc|L}}- prefixes are also used with other monosaccharides, to distinguish two particular stereoisomers that are mirror-images of each other. For this purpose, one considers the chiral carbon that is furthest removed from the C=O group. Its four bonds must connect to −H, −OH, −CH<sub>2</sub>(OH), and the rest of the molecule.  If the molecule can be rotated in space so that the directions of those four groups match those of the analog groups in {{sc|D}}-glyceraldehyde's C2, then the isomer receives the {{sc|D}}- prefix. Otherwise, it receives the {{sc|L}}- prefix.

In the Fischer projection, the {{sc|D}}- and {{sc|L}}- prefixes specifies the configuration at the carbon atom that is second from bottom: {{sc|D}}- if the hydroxyl is on the right side, and {{sc|L}}- if it is on the left side.

Note that the {{sc|D}}- and {{sc|L}}- prefixes do not indicate the direction of rotation of polarized light, which is a combined effect of the arrangement at all chiral centers.  However, the two enantiomers will always rotate the light in opposite directions, by the same amount. See also [[Absolute configuration#By relative configuration: D- and L-|{{sc|d/l}} system]].