Purity optical

Optical purity is defined by the terms enantiomeric excess(tt) and diastereoisomeric excess de) given by the formula shown below. 

Most naturally occurring molecules that contain one stereogenic center exist as one enantiomer. Samples that contain only one enantiomeric form are optically puie. Naturally occurring cholesterol, for example, exists only as the (-) form. It rotates hght in a counterclockwise direction. However, compounds synthesized in the laboratory may not all have the same handedness, and the reaction yields a mixture of two enantiomers. 

What is the optical rotation of a mixture of enantiomers, and how is it related to the percentage of each enantiomer in the mixture When plane-polarized hght interacts with a single enantiomer of a chiral molecule, the plane is rotated in one direction. If the plane-polarized hght interacts with the other enantiomer, the plane is rotated in an equal and opposite direction. If a solution contains equal amounts of two enantiomers, the clockwise and counterclockwise rotations resulting from all molecules 

Now consider a circumstance in which the percent ratio of a mixture of enantiomers is not 50 50. The percent enantiomeric excess of the enantiomer present in the larger amount is calculated as follows. 

The percent enantiomeric excess is the optical purity of the sample. For example, a 60 40 ratio of (+)-2-iodobutane and (-)-2-iodobutane is 20% optically pure. This value indicates that the rotation of the (-) isomer (40% of the total) cancels the rotation of some of the (+) isomer (40% of the total). The remaining 20% of the sample, which is (+)-2-iodobutane, is responsible for the observed rotation, so the sample is 20% optically pure. 

What is [a]j of the enantiomer of naturally occurring testosterone (See Table 8.1.) What is the name of this enantiomer  

As the metal atoms in organo-transition-metal compounds often have 18-electron configurations, the compounds are diamagnetic and give sim- 

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Mixtures containing equal quantities of enantiomers are called racemic mixtures Racemic mixtures are optically inactive Conversely when one enantiomer is present m excess a net rotation of the plane of polarization is observed At the limit where all the molecules are of the same handedness we say the substance is optically pure Optical purity or percent enantiomeric excess is defined as... 

An advantage that sulfonate esters have over alkyl halides is that their prepara tion from alcohols does not involve any of the bonds to carbon The alcohol oxygen becomes the oxygen that connects the alkyl group to the sulfonyl group Thus the configuration of a sulfonate ester is exactly the same as that of the alcohol from which It was prepared If we wish to study the stereochemistry of nucleophilic substitution m an optically active substrate for example we know that a tosylate ester will have the same configuration and the same optical purity as the alcohol from which it was prepared... 

The same cannot be said about reactions with alkyl halides as substrates The conver Sion of optically active 2 octanol to the corresponding halide does involve a bond to the chirality center and so the optical purity and absolute configuration of the alkyl halide need to be independently established... 

One of the newer and more fmitful developments in this area is asymmetric hydroboration giving chiral organoboranes, which can be transformed into chiral carbon compounds of high optical purity. Other new directions focus on catalytic hydroboration, asymmetric aHylboration, cross-coupling reactions, and appHcations in biomedical research. This article gives an account of the most important aspects of the hydroboration reaction and transformations of its products. For more detail, monographs and reviews are available (1—13). 

EinaHy, kinetic resolution of racemic olefins and aHenes can be achieved by hydroboration. The reaction of an olefin or aHene racemate with a deficient amount of an asymmetric hydroborating agent results in the preferential conversion of the more reactive enantiomer into the organoborane. The remaining unreacted substrate is enriched in the less reactive enantiomer. Optical purities in the range of 1—65% have been reported (471). 

High demands are placed on the substrate material of disk-shaped optical data storage devices regarding the optical, physical, chemical, mechanical, and thermal properties. In addition to these physical parameters, they have to meet special requirements regarding optical purity of the material, processing characteristics, and especially in mass production, economic characteristics (costs, processing). The question of recyclabiUty must also be tackled. 

The oil possesses moderate antibacterial and strong antifungal properties. Thus the appHcation of the oil to the cmst of cheese could serve to prevent the formation of mycotoxia ia the cheese. The optical purity of the carvone ia caraway has been determined usiag a chiral gc column (72). It was found to be (i )(+) = 97.64% and (5 )(—) = 2.36%. 

Optically Active PO. The synthesis of optically pure PO has been accompHshed by microbial asymmetric reduction of chloroacetone [78-95-5] (90). (3)-2-Meth5loxirane [16088-62-3] (PO) can be prepared in 90% optical purity from ethyl (3)-lactate in 44% overall yield (91). This method gives good optical purity from inexpensive reagents without the need for chromatography or a fermentation step. (3)-PO is available from Aldrich Chemical Company, having a specific rotation [0 ] ° 7.2 (c = 1, CHCl ). 

Garene Manufacture. 3-Carene is obtained by fractional distillation of turpentine. Turpentine from the western United States and Canada averages about 25% 3-carene much of it is unutilised although it is obtained in high optical purity. Turpentines from the Scandinavian countries, the CIS, Pakistan, and India all contain significant quantities of 3-carene. 

Fig. 2. Chromatogram showing (a) the Ic separation of A, (+) (T)-(l-ferrocenyl-ethyl)thioethanol B, (+) 1-ferrocenyl-l-methoxyethane and C, (+) 1-mthenocenylethanol, on a 25-cm P-cyclodextrin column (see Table 2), and (b) the potential use of a P-cyclodextrin column to determine optical purity...

Both saturated (50) and unsaturated derivatives (51) are easily accepted by lipases and esterases. Lipase P from Amano resolves azide (52) or naphthyl (53) derivatives with good yields and excellent selectivity. PPL-catalyzed resolution of glycidyl esters (54) is of great synthetic utiUty because it provides an alternative to the Sharpless epoxidation route for the synthesis of P-blockers. The optical purity of glycidyl esters strongly depends on the stmcture of the acyl moiety the hydrolysis of propyl and butyl derivatives of epoxy alcohols results ia esters with ee > 95% (30). 

Resolution of Racemic Amines and Amino Acids. Acylases (EC3.5.1.14) are the most commonly used enzymes for the resolution of amino acids. Porcine kidney acylase (PKA) and the fungaly3.spet i//us acylase (AA) are commercially available, inexpensive, and stable. They have broad substrate specificity and hydrolyze a wide spectmm of natural and unnatural A/-acyl amino acids, with exceptionally high enantioselectivity in almost all cases. Moreover, theU enantioselectivity is exceptionally good with most substrates. A general paper on this subject has been pubUshed (106) in which the resolution of over 50 A/-acyl amino acids and analogues is described. Also reported are the stabiUties of the enzymes and the effect of different acyl groups on the rate and selectivity of enzymatic hydrolysis. Some of the substrates that are easily resolved on 10—100 g scale are presented in Figure 4 (106). Lipases are also used for the resolution of A/-acylated amino acids but the rates and optical purities are usually low (107). 

An increasing number of examples of ring formation through 1,5-electrocyclization of appropriate carbanions are illustrated in Scheme 27. In the last example the use of a chiral alkoxide (R = menthyl or bornyl) results in the formation of chiral indolines with optical purities ranging from 17 to 31%. 

Transition metal-catalyzed epoxidations, by peracids or peroxides, are complex and diverse in their reaction mechanisms (Section 5.05.4.2.2) (77MI50300). However, most advantageous conversions are possible using metal complexes. The use of t-butyl hydroperoxide with titanium tetraisopropoxide in the presence of tartrates gave asymmetric epoxides of 90-95% optical purity (80JA5974). 

Diaziridine (33) was obtained with more than 90% optical purity by separation of the a-phenylethylamine salts (76IZV1898). 

The resolution of sec.-octyl alcohol was first described by Pickard and Kenyon. The method employed by these authors differed from the foregoing in the following respects. The brucine salt of sec.-octyl hydrogen phthalate was crystallized several times from acetone until it reached optical purity and was then decom-... 

Pure miantiomeric substances show rotations that are equal in magnitude but opposite in direction. Unequal mixtures of enantiomers rotate light in proportion to the composition. The relationship between optical purity and measured rotation is... 

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