Configuration of tartaric acids

Chemical Properties. The notation used by Chemical Abstracts to reflect the configuration of tartaric acid is as follows (R-R, R )-tartaric acid [S7-69A-] (4) (S-R, R )-tartaric acid [147-71-7] (5) and y j O-tartaric acid [147-73-9] (6). Racemic acid is an equimolar mixture of the two optically active enantiomers and, hence, like the meso acid, is optically inactive. 

A serious ambiguity arises for compounds such as the active tartaric acids. If the amino-acid convention is used, (+)-tartaric acid falls in the d series by the sugar convention, it has the l configuration. One way out of this dilemma is to use the subscripts, v and g to denote the amino-acid or carbohydrate conventions, respectively. Then the absolute configuration of (+)-tartaric acid can be designated as either Ds-(+)-tartaric acid of lb-(+)-tartaric acid. 

If more than one chiral center is present, the configuration at each is specified by the symbol R or S together with the number of the chiral atom. Thus the configuration of (+)-tartaric acid is known to be that designated in the name (2R,3R)-(+)-tartaric acid ... 

We now consider the other configurations of tartaric acid, i.e. (2R,3S) 9 and (2S,3R ) 10. Here, the presence of identical sets of substituents at C(2) and C(3) brings about a difference from the general case which was shown by 1. Inspection of 9 and 10 reveals that 10 is a mirror image of 9 (and vice versa). However, 9 and 10 are identical and superimposable. 

Relationship between absolute configurations of tartaric acid and glyceraldehydes... 

The distinction between the various configurations of monocentric, tetrahedral molecules is dependent on the ability to differentiate between all four ligands. In systems with more than one asymmetric C-atom these can be regarded as the chiral subunits of the total configuration. If there is sufficient flexibility one can expect 2n configurations with n different asymmetric C-atoms. If there are asymmetric C-atoms of the same kind, as in the isomers of tartaric acid, a lower number of distinguishable configurations is encountered. 

The foundation for the configuration of these amino acids will be obtained if a-amino-y8-chloropropionic acid can be converted into aspartic acid, the configuration of which is known from its relationship to malic acid, (d-aspartic acid is converted into d-malic acid by nitrous acid.) The configuration of malic acid can be referred to that of tartaric acid and thence to d-glucose. 

Shortly after the first announcement of optical resolution of ( )-cyclooctene, Moscowitz and Mislow 13) published a communication in which, on the basis of their MO calculation/they assigned the (S)-configuration to the (—)-enantiomer. Eventually, this conclusion was proved wrong 14,15) and the opposite configuration was assigned when the absolute configuration of (—)-( )-cyclooctene was shown to be directly correlated with that of (+)-tartaric acid 16a,b). 

Osmium tetroxide oxidation of (- )-( )-cyclooctene (6) afforded the ( + )-diol 7 whose absolute configuration was related to that of (+ )-tartaric acid (9) via the (+)-dimethoxy derivative 8. The (R)-configuration assigned by this correlation has been confirmed by a number of direct or indirect approaches. 

Now we do know. X-ray crystallographic studies in 1951 confirmed that the levorotatory and dextrorotatory forms of tartaric acid are mirror images of each other at the molecular level and established the absolute configuration of each (Fig. 1). The same approach has been used to demonstrate that although the amino acid alanine has two stereoisomeric forms (designated d and l), alanine in proteins exists exclusively in one form (the l isomer see Chapter 3). 

An elaborate network connecting signs of rotation and relative configurations was developed that included the most important compounds of organic and biological chemistry. When, in 1951, the absolute configuration of a salt of (+)-tartaric acid was... 

The X-ray diffraction patterns show that the materials obtained from the various configurational isomers of tartaric acid have different architectures. Both are hexagonal columnar mesophases, but, whereas the data for (LP2, LU2) are consistent with columns formed by three polymeric strands having a triple helix superstructure (Figure 41), those for the (MP2, MU2) mixture fit a model built on three strands in a zig-zag conformation. The LD mixture has another arrangement again. 

Diastereoselective alkylation of tartaric acid. The enolate (2) of the acetonide of dimethyl (R, R)-tartrate (1) can be generated with LDA in THF-HMPT at — 70° and is sufficiently stable for alkylation with allyl and benzyl halides, but not with other simple alkyl halides, and for addition to acetone (60% yield). The main products (3) of allylation and benzylation have the /ranr-configuration, and thus the substitution occurs with retention of configuration.7... 

The relative configurations of the stereoisomers of tartaric acid were established by the following syntheses ... 

In 1951, it became possible to determine whether Rosanoff s guess was right. Ordinary X-ray crystallography cannot distinguish between a d and a l isomer, but by use of a special technique, Bijvoet was able to examine sodium rubidium tartrate and found that Rosanoff had made the correct choice. It was perhaps historically fitting that the first true absolute configuration should have been determined on a salt of tartaric acid, since Pasteur made his great discoveries on another salt of this acid. 

To determine the absolute configuration of optically active organic compounds, there are two nonempirical methods. One is the Bijvoet method in the X-ray crystallographic structure analysis, which is based on the anomalous dispersion effect of heavy atoms. - The X-ray Bijvoet method has been extensively applied to various chiral organic compounds since Bijvoet first succeeded in determination of the absolute stereochemistry of tartaric acid in 1951. The second method is a newer one based on the circular dichroism (CD) spectroscopy. Harada and Nakanishi have developed the CD dibenzoate chirality rule, a powerful method for determination of the absolute configuration of glycols, which was later generalized as the CD exciton chirality method. 8 The absolute stereochemistry of various natural products has been determined by application of this nonempirical method. 

The meso stereoisomer of tartaric acid is achiral, and possesses two self-cancelling stereogenic centres of opposite configuration. 

Draw all the stereoisomers of each of the molecules (a)- e) assign configuration to stereogenic centres and say whether each stereoisomer is chiral (a) 2,3-dibromobutane (b) 2-bromo-3-chlorobutane (c) the monomethyl ester of tartaric acid (2,3-dihy-droxybutanedioic acid) (d) 2,3-difluoropentane (e) 1,3-dichloro-cyclopentane. 

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