Symmetrical reagents do not differentiate between the members of a pair of enantiomers for the same reason that an ordinary sock fits equally well on a right foot as on a left foot. Meso configurations and draw the configurations for each of them.ĥ-6 SOME EXAMPLES OF THE IMPORTANCE OF STEREOISOMERISM TO BIOLOGY. Listed select all those that may have achiral Which stereoisomers are enantiomers? Which are diastereomers? What combination of isomers would give a racemic mixture? Which isomer is achiral? An example is offered by the meso forms of tetrahydroxyhexanedioic acid which, with four chiral atoms, have configurations 28 and 29:Įxercise 5-13 Write structures for all the configurations possible for 2,4-dibromo- pentane. At most, one meso compound is possible for structures with two chiral centers, whereas two are possible for structures with four chiral centers. For every meso form there will be one less pair of enantiomers and one less total number of possible configurations than is theoretically possible according to the number of chiral centers. The idea that for every n chiral centers there can be 2" different configurations will be true only if none of the configurations has sufficient symmetry to be identical with its mirror image. For a molecule with chiral centers, if its projection formula hasĪ plane of symmetry or if we can find a rotational conformation with either a plane or center of symmetry, then it will be meso and achiral. Another way of putting it is that each half of the molecule is the photographic image (i.e., reverse) of the other half.
Thus a line drawn at any angle through the midpoint of the central C-C bond of 25a (or 26a) has an identical environment on each side of the midpoint. In this confermation, the molecules do have a center of symmetry. If you make models of 25a and 26a you will find that they are mirror images and * identical but, as we have said, they have no plane of symmetry. There is another symmetry test for meso configurations that is applicable to staggered conformations and can be illustrated with the tartaric acids.
Mations and also whether this tartaric a c ~ d IS meso-tartar~cac~d,an opt~callyactlve tartaric a c ~ dor, racemic a c ~ dGive your reasoning
5-5A Meso Compounds (Achiral Diastereorners)