Enantiomers chiral Objects that are nonsuperposable on their mirror images are chiral (from the Greek: cheir, hand). –They show handedness. The most common cause of enantiomerism in organic molecules is the presence of a carbon with four different groups bonded to it. stereocenter –A carbon with four different groups bonded to it is called a stereocenter.
Multiple Chiral Centers n 2 n For a molecule with n stereocenters, the maximum number of possible stereoisomers is 2 n. –We have already verified that, for a molecule with one stereocenter, 2 1 = 2 stereoisomers (one pair of enantiomers) are possible. –For a molecule with two stereocenters, a maximum of 2 2 = 4 stereoisomers (two pair of enantiomers) are possible. –For a molecule with three stereocenters, a maximum of 2 3 = 8 stereoisomers (four pairs of enantiomers) are possible, and so forth.
2R,3S 2S,3R 2R,3R 2S,3S The Four Stereoisomers of a Simple sugar
Chirality of Biomolecules –Because interactions between molecules in living systems take place in a chiral environment, a molecule and its enantiomer or one of its diastereomers elicit different physiological responses. –As we have seen, (S)-ibuprofen is active as a pain and fever reliever, while its R enantiomer is inactive. –The S enantiomer of naproxen is the active pain reliever, but its R enantiomer is a liver toxin!