D-glucose and L-glucose are not epimers; they are actually enantiomers. They are mirror images of each other and are optically active, rotating plane-polarized light in opposite directions. The designation of D and L in glucose refers to the configuration of the hydroxyl group attached to the chiral center farthest from the carbonyl group (C5 in glucose). D-glucose has the hydroxyl group on the right side in the Fischer projection, while L-glucose has it on the left side.
D-glucose and L-glucose are enantiomers rather than epimers because they differ in the spatial arrangement around all of their chiral centers, not just at one specific carbon atom. Enantiomers are a specific type of stereoisomers that are non-superimposable mirror images of each other, meaning they have opposite configurations at every chiral center in the molecule.
D-glyceraldehyde and L-glyceraldehyde, on the other hand, are epimers. They are stereoisomers that differ in configuration at only one specific chiral center—the carbon atom closest to the aldehyde group (C2 in glyceraldehyde). D-glyceraldehyde has the hydroxyl group on the right side in the Fischer projection, while L-glyceraldehyde has it on the left side. This difference at one chiral center classifies them as epimers.
In the case of glucose, D-glucose and L-glucose are enantiomers. They have identical molecular formulas and structures but differ in their three-dimensional spatial arrangements, resulting in distinct optical properties. Enantiomers like D-glucose and L-glucose have different biological activities and metabolic pathways due to their mirror-image configurations, which affect their interactions with enzymes and receptors in living organisms.