Optical isomeres

Naturally Derived Materials. The following are descriptions of some of the most important naturally derived materials in use. Importance in this context is defined in terms of the total value of the materials, which range from expensive, low volume materials that have great aesthetic value to relatively inexpensive and widely used products. Eor some of the naturals, it is indicated whether they can be distilled to provide individual chemicals for use as such or as intermediates. Materials produced in this way from a given natural source are usually not interchangeable with those from other naturals or synthetics. In some cases this may be due to optical isomerism, which can have a significant effect on odor, but usually it is due to trace impurities. 

Gitronellol Manufacture. CitroneUol is found widely in nature and in both optically isomeric forms. Prior to the development of synthetic citroneUol, this alcohol was obtained from certain oils of the Kosaceae family or by hydrogenation of citroneUal isolated from citroneUa oil. CitroneUol has a floral odor resembling that of roses. 

A few cases of optical isomerism are known for planar and tetrahedral complexes involving unsymmetrical bidentate ligands, but by far the most numerous examples are afforded by octahedral compounds of chelating ligands, e.g. [Cr(oxalate)3] and [Co(edta)] (Fig. 19.13). 

A. R. Cushny, Biological relations of optically isomeric substances, Balliere, Tindall and Cox, London, 1926. 

Which of the following compounds can show optical isomerism ... 

Chromium, tris(hexafluoroacetylacetonato) optical isomerism, 1, 28 Chromium, tris(oxalato)-raceinization solid state, 1,466 strychnine salt... 

Cobalt, cis-chloroamminebis(l, 2-ethanediamine)-optical isomerism, 1,12 Cobalt, chlorobis(l,2-ethanediamine)-solvation, 1,503... 

Cobalt, tris(tetraaminine-p-dihydroxocobalt)-optical isomerism, 1,13... 

One-dimensional complexes, 6,134 One-dimensional conductors, 6,134 One-dimensional metals Krogmann salts, 6, 136 Optical isomerism cobalt ammines, 1,12 history, 1,180... 

Many substances exhibit the property of isomerism they occur in two or more molecular forms that have the same composition but differ from each other in structure and in their properties. One type of isomerism, known as optical isomerism, is exhibited by molecules that have the same constituent atoms but are arranged in different spatial distributions, where one of the optical isomers is a mirror image of the other (see Textbox 63). 

The main constituents of spearmint oil are /-carvone (Fig. 13.12.7) and /-limonene (Fig. 13.12.8). Oil of spearmint contains from 45 to 60% l-carvone, 6 to 20% of alcohols, and 4 to 20% of esters and terpenes, mainly /-limonene and cineole (see Fig. 13.12.4)J2J The optically isomeric form of carvone, d-carvone, is found in oil of caraway and oil of dill. Carvone appears to co-occur with limonene when present in a plant. 

The second type of stereoisomerism is optical isomerism, in which two molecules that are mirror images of each other are not superimposable on each other. Consider the compound 2-butanol, CH3CH(OH)CH2CH3. It has two optical isomers, because it is not superimposable on its mirror image. 

Optical isomerism is exhibited by compounds that are chiral, i.e., are not superimposable on their mirror images. Such a compound and its mirror image are called optical isomers or enantiomers. They have identical physical and chemical properties except when they interact with other chiral molecules. 

Optical Isomerism of (D-L-Isomerism) and Tacticity of Polymers Optical isomerism has its origin in the way different substituents occupy positions on an asymmetric carbon atom in a polymer molecule. For example, polyethylene molecule has fully saturated carbon atoms as shown in the following chemical formula ... 

---