Achiral meso compound

When the bromonium ions react by either path (a) or path (b), they yiled the same achiral meso compound. [Reaction of the enantiomer of the intermediate bromonium ion would produce the same result.]... 

You could have said that there are four stereoisomers but the following statement is much more helpful. There are three diastereoisomers, the syn,syn, the yn,anti, and the anti,anti. The syn,syn and the anti,anti are achiral (meso) compounds but the syn,anti is chiral and has two enantiomers,... 

The chirality of (d) depends on the configuration at both of the chirality centers. The (R.R) and (5,5) isomers are chiral enantiomers the (R,S) isomer is an achiral meso compound. 

Because one stereoisomer of 1,3-dibromocyclopentane is superimposable on its mirror image, there are only three stereoisomers, not four. A is an achiral meso compound and B and C are a pair of chiral enantiomers. A and B are diastereomers, as are A and C. 

The physical properties of A and B differ from their diastereomer C. The physical properties of a racemic mixture of A and B (last column) can also differ from either enantiomer and diastereomer C. C is an achiral meso compound, so it is optically inactive [a] - 0. 

To draw each product of epoxidation, add an O atom from either side of the alkene, and keep all substituents in their original orientations. The cis methyl groups in c/s-2-butene become cis substituents in the epoxide. Addition of an O atom from either side of the trigonal planar alkene leads to the same compound—an achiral meso compound that contains two stereogenic centers. 

The two cis COOH groups of maleic acid become two ds substituents in a Diels—Alder adduct. The COOH groups can be drawn both above or both below the plane to afford a single achiral meso compound. The trans dienophUe fumaric acid yields two enantiomers with trans COOH groups. 

As BC can attack either carbon atom of the bromonium ion, reaction with Z-but-2-ene produces a 1 1 mixture of enantiomers (only the 2R,3R isomer is shown above). For -but-2-ene, the attack of Be at either carbon atom of the bromonium ion produces the same compound. This compound has a plane of symmetry and hence is an achiral meso compound. 

This holds for acyclic compounds as well. We have just seen that 2,3-dibromo-butane is an achiral meso compound because it has a plane of symmetry. To see that it had a plane of symmetry, however, we had to look at a relatively unstable eclipsed conformer. The more stable staggered conformer does not have a plane of symmetry. 

A meso compound contains two or more chiral centers bonded in such a way that it is achiral. Meso compounds usually have an internal plane of symmetry. 

We already know from Section 4.8 that finding four different groups attached to one carbon is not a sufficient condition for chirality. There are achiral meso compounds that satisfy this condition. But is the presence of a carbon atom attached... 

Even though they are achiral, meso compounds are of some value as substrates in asymmetric synthesis, since, upon enantioselective reaction, they give chiral products with two contiguous stereogenic centres (see sections 6.5.2 and 6.5.3). 

This synthesis of the lactone portion illustrates how an esterase enzyme can distinguish between two enantiotopic groups in an achiral meso compound to provide an enantiomerically enriched chiral product. 

The cis isomer is superimposable on its mirror image, making them identical. Thus, A is an achiral meso compound. 

Tartaric acid (systematic name 2,3-dihydroxy-butanedioic acid) is a naturally occurring dicarboxylic acid containing two stereocenters with identical substitution patterns. Therefore it exists as a pair of enantiomers (which have identical physical properties but which rotate plane-polarized light in opposite directions) and an achiral meso compound (with different physical and chemical properties from those of the chiral diastereomers). 

All four compounds are identical—an achiral meso compound. 

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