Enantiomers, racemic

J. Jacques, A. CoUet, and S. H. Wilen, Enantiomers, Racemates, and Resolutions, Wiley, New York, 1981. 

J. Jaques, A. CoUet, and S. WiUen, Enantiomers, Racemate, and Resolutions,]o m Wiley Sons, Inc., New York, 1981 The Chemical Society of Japan, eds., Kikan Kagaku Sosetsu (No. 6, Resolution of Optical Isomers), Gakkai Shuppan Senta, Tokyo, Japan, 1989 G. C. Barrett ia Ref. 1, Chapt. 10, pp. 338—353 S. Otsuka and T. Mukaiyama, Progress of ylsymmetric Synthesis and Optical Resolution (ia Japanese), Kagaku Dojia, Kyoto, Japan, 1982. 

Jacques, I., Collet, A. and Wilen, S.H., 1981. Enantiomers, Racemates and Resolutions. New York John Wiley Sons, Reprinted, 1991. 

In general, high selectivities can be obtained in liquid membrane systems. However, one disadvantage of this technique is that the enantiomer ratio in the permeate decreases rapidly when the feed stream is depleted in one enantiomer. Racemization of the feed would be an approach to tackle this problem or, alternatively, using a system containing the two opposite selectors, so that the feed stream remains virtually racemic [21]. Another potential drawback of supported enantioselective liquid membranes is the application on an industrial scale. Often a complex multistage process is required in order to achieve the desired purity of the product. This leads to a relatively complicated flow scheme and expensive process equipment for large-scale separations. 

Meso compounds contain chirality centers but are achiral overall because they have a plane of symmetry. Racemic mixtures, or racemates, are 50 50 mixtures of (+) and (-) enantiomers. Racemic mixtures and individual diastereomers differ in their physical properties, such as solubility, melting point, and boiling point. 

In any reaction, the mechanism should explain not only the regiochemistry, but the stereochemistry as well. In this particular reaction (addition of H—X across alkenes), the stereochemistry is generally not relevant. Recall from the previous section that we need to consider stereochemistry (syn vs. anti) only in cases where the reaction generates two new stereocenters. If only one stereocenter is formed, then we expect a pair of enantiomers (racemic mixture), regardless of whether the reaction was anti or syn. You will probably not see an example where two new stereocenters are formed, because the stereochemical outcome in such a case is complex and is beyond the scope of our conversation. 

Jacques, J. Collet, A. Wilen, S. H. "Enantiomers, Racemates and Resolutions," Wiley-Interscience, New York, 1981. 

Define plane-polarized light, optical rotation, optical activity, asymmetric carbon atom, enantiomers, racemic mixture, polarimeter, and specific rotation. 

Samples of 2-butanol are not optically active because they are actually equal mixtures of two enantiomers (racemic mixtures), so their optical rotations cancel out. 

Disubstituted (cyclobutadiene)Fe(CO)3 complexes in which the two substituents are different may exist as enantiomers. Racemic cyclobutadiene carboxylic acids or cyclobutadiene amine complexes of this type have been separated by classical resolution methodology234. These optically active (cyclobutadiene)Fe(CO)3 complexes are stable with respect to racemization at 120°C for 24 h. This stability contrasts with acyclic... 

One may consider a series of physical states ranging from the crystalline, where molecular aggregation and orientation are large, to the dilute gaseous state, where there are no significant orientational limits. States of intermediate order are represented by micelles, liquid crystals, monolayers, ion pairs, and dipole-dipole complexes. In the crystalline state, the differences between pure enantiomers, racemic modifications, and diastereomeric complexes are clearly defined both structurally and energetically (32,33). At the other extreme, stereospecific interactions between diastereomerically related solvents and solutes, ion pairs, and other partially oriented systems are much less clearly resolved. 

Grosch B, Bach T (2004) In Horspool W, Lend F (eds) CRC handbook of organic photochemistry and photobiology, 2nd edn. CRC, Boca Raton, chap 61 Mori T, Inoue Y (2004) In Horspool W, Lend F (eds) CRC handbook of organic photochemistry and photobiology, 2nd edn. CRC, Boca Raton, chap 16 Caswell L, Garcia-Garibay M, Scheffer JR, Trotter J (1993) J Chem Ed 70 785 Jacques J, Collet A, Wilen SH (1981) Enantiomers, racemates and resolutions. WUey, New York... 

Jacques,J., A.Collet and S.H.Wilen Enantiomers, Racemates and Resolutions , p.217, John Wiley Sons, Inc., New York (1981)... 

For a monograph on the properties of racemates and their resolution, see Jacques Collet Wilen Enantiomers, Racemates, and Resolutions Wiley New York, 1981. 

In connection with the preparation of (+)- and (-)-tetrahydroharmine (compounds 39 and 40 in Fig. (10), respectively) the racemization of these compounds was studied by Chnsey and Brossi [34]. They demonstrated that, under acidic conditions, the pure enantiomers racemized with relative ease, and suggested that the racemization resembled epimerization of reserpine (1) and 1,3-disubstituted tetrahydro-P-carbolines. Therefore, the mechanism responsible for the racemization would be one of those mentioned above. 

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