Lactic acid Stereo-isomerism

This then, is the van t Hoff-LeBel Theory of Stereo-isomerism known also as the Theory of the Asymmetric Carbon Atom or as the Tetrahedral Theory. The theory is supported by a large number of facts and has been fruitful in leading to new discoveries. We shall find cases of stereo-isomerism in several of the classes of compounds which we shall study and some of our most common substances, such as lactic acid,... 

The existence of three stereo-isomeric lactic acids is therefore explained in exactly the same way as the three stereo-isomers in the case of active amyl alcohol, 2-methyl butanol-1 (p. 90). We need not repeat the discussion of stereo-isomerism as explained by the van tHoff-LeBel theory of the asymmetric carbon atom, i.e., the tetra-hedral theory. The discussion as previously given for the amyl alcohols, applies exactly in the present case. 

Stereo Isomerism of Malic Acid.—On examination of the formula of malic acid it will be seen that one of the carbons is asymmetric i.e.j it has united to it four different elements or groups, viz., (—H), (—OH), (—COOH), and (—CH2—COOH). We should, therefore, expect to find that malic acid is optically active and that it exists in the three forms of dextroj levo, and inactive. This is in accordance with the facts. The formulas for the three stereo-isomeric forms of malic acid may be written as follows, corresponding exactly to those for lactic acid. 

The study of malic acid in connection with its stereo-isomerism, together with the similar study of the related acids, lactic, tartaric, maleic and fumaric has been of the greatest importance in establishing our ideas of stereo-isomerism. 

It is this fourth unresolvable inactive tartaric acid which gives to tartaric acid its especial interest and importance in connection with the theory of stereo-isomerism. This acid, like the other three, has been fully explained in accordance with the tetra-hedral theory of van t Hoff and LeBel. The explanation rests upon the fact that there is a second asymmetric carbon atom in tartaric acid. We may construct, by models, or, by drawings, space-formulas for tartaric acid. According to the tetra-hedral theory, the dextro, levo and racemic inactive forms will be as follows, analogous to the corresponding formulas for the three lactic acids. The meso-tartaric acid is represented by the third drawing. 

Palade et al, 2001). The stereo-isomeric l/d ratio of the lactate unit association influenced PLA properties (Tsuji and Ikata, 1992). There are three types of PLAs because there are two stereoisomeric forms of lactic acid, poly (levo-lactic acid) and poly (dextro-lactic acid), which are both semi-crystalline and have identical chemical and physical properties. Poly (D,L-lactic acid) or poly (meso-lactic acid), a racemic polymer obtained from an equimolar mixture of D- and L- lactic acid, is amorphous, with weak mechanical properties. The... 

Isomerism of Tartaric Acid.—Examination of the formula for tartaric acid, which, by the facts given above, has its constitution fully established as symmetrical di-hydroxy succinic acid, shows the interesting fact that there are present two asymmetric carbon atomsy and that each of these has linked to it the same set of four different groups. We should, therefore, expect to find tartaric acid existing in the dextrOy the levo and the inactive forms. The stereo-chemical formulas similar to those of lactic and malic acids we may write as follows. 

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