Absolute configuration of tartaric acid

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. 

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

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. 

Due to the complexity of conformational equilibria, the application of the dibenzoate chirality rule to determination of the absolute configuration of acyclic diols and polyols requires cautious evaluation of the CD data. For example, (0,0)-dibenzoyl derivatives of diesters and N.N.N ,AT-tetraalkyldiamides of (/t,f )-tartaric acid give exciton Cotton effects of opposite sign due to the preference of diesters for a planar and tetraalkyldiamides for a gauche conformation of the carbon chain176. 

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... 

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. 

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