Lactic acid specific rotation

Specific rotation is a physical property of a substance just as melting point boil mg point density and solubility are For example the lactic acid obtained from milk is exclusively a single enantiomer We cite its specific rotation m the form [a]o =+3 8° The temperature m degrees Celsius and the wavelength of light at which the measure ment was made are indicated as superscripts and subscripts respectively... 

In general, small specific rotations should be expected for such adamantane derivatives since a large reduction in optical rotatory power should occur when pairwise interactions are greatly reduced by distance. The resolution of several tetrasubstituted adamantanes (62-65) has been attempted 178 179> 247f Mes-ured rotations, as expected 4> are quite low. Only 65, the formal analogue of lactic acid, has been proven to be optically active 178>179f by a confirmatory approach. 

When optical rotation data arc expressed in this standard way, the specific rotation, lain, is a physical constant characteristic oTa given opticall> active compound- For example, the (e > lactic acid Uiat we saw in Section 9.1 has al > +3.82 , and (—> Iactic acid has loin -S-Blf - Some additional examples are listed in Table 9 l. 

Levo Lactic Acid.— Levo lactic acid was first obtained by the fermentation of cane sugar by specific bacteria. It is levo rotatory but, like the dextro acid, the rotation of its salts and its anhydride is reversed, being dextro rotatory. The levo lactic acid and also the dextro acid may be obtained by splitting the inactive acid into its optical components by means of its strychnine salt. 

The monomers of L- and D-lactic acids, LLA, and DLA, and their homopolymers, PLLA and PDLA, are optically active. The specific optical rotation ([aj sse) values of PLLA and PDLA... 

Lactic acid is an optically active hydroxyacid that is important in several biological processes. It has one stereogenic center. Its structure and some of its properties are shown in Figure 5.10. Note that both enantiomers have identical melting points and, except for sign, identical specific rotations. 

The chirality of lactic acid often results in confusion regarding nomenclature. A number of different names are used in the literature. This confusion is the result of mixing the molecular structure and a physical property (optical rotation). (5 )-Lactic acid (or L-lactic acid) has a slightly positive specific optical rotation and is frequently named L-( -h )-lactic acid [14]. However, a concentrated solution of (5 )-lactic acid at equilibrium contains lactic acid oligomers, which results in an overall negative optical rotation. Therefore, it is advised to use the structural RIS notation or the older notation of l and d and avoid the -h and — of the optical rotation (Table 1.1). 

S)-Lactic acid has a specific rotation of +3.8. (a) If the ee of a solution of lactic acid is 60%, what is [a] for this solution (b) How much of the dextrorotatory and levorotatory isomers does the solution contain ... 

Lactic acid in the blood has a specific rotation of +2.6°. A sample of lactic acid obtained from sour milk has a specific rotation of —2.6°. How do these compounds differ ... 

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