Vocabulary of Stereochemistry and Stereoselective Synthesis

Molecules of the same empirical formula are either identical or isomers. Isomers either differ in the connectivity of their constituent atoms—this then involves constitutional isomers (structural isomers)—or they do not differ in this way then they are stereoisomers. Stereoiso- 

According to the foregoing analysis, conformers such as gauche- and anri-butane or chair and twist-boat cyclohexane would be considered to be diastereomers of each other. However, under most conditions these conformers interconvert so rapidly that butane and cyclohexane are considered to be single species and not mixtures of stereoisomers. When we have to write chemistry books for people living on the outer planets of the solar system, we might have to modify these concepts. 

Let us also visualize the important concept of chirality. Only molecules that differ from their mirror image have enantiomers. Molecules of this type are called chiral. For anything to be chiral, that is, non-superimposable on its mirror—there is a necessary and sufficient condition it is the absence of an intramolecular rotation/reflection axis. What s that, you say See the next paragraph. 

According to the foregoing definition, chirality occurs only in molecules that do not have a rotation/reflection axis. However, if the molecule only has an axis ofrotation, it is chiral. For 

A reaction that takes place preferentially or exclusively at one functional group among several takes place with chemoselectivity. A reaction that preferentially gives one of several conceivable stereoisomers is referred to as moderately or highly stereoselective, depending on the extent of stereoselectivity. When these conceivable stereoisomers are diastereomers, we have diastereoselective reaction and the occurrence of diastereoselectivity. When the conceivable stereoisomers are enantiomers, we have an enantioselective reaction, or enantioselectivity. 

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Vocabulary of Stereochemistry and Stereoselective Synthesis II Topicity, Asymmetric Synthesis... 

Gunter Helmchen Nomenclature and Vocabulary of Organic Stereochemistry, in Methods of Organic Chemistry (Houben-Weyl), Volume E21a, Stereoselective Synthesis, Thieme, Stuttgart, New York, 1995, pp. 1-74... 

Helmchen G (1996) A. General aspects. 1. Nomenclature and vocabulary of organic stereochemistry. In Helmchen G, Hoffinann RW, Mulzer J, Schaumann E (eds) Stereoselective Synthesis. Methods of Organic Chemistry (Houben-Weyl), Workbench Edition E21, vol 1,4th edn. Georg Thieme, Stuttgart, New York, pp 1-74 Hirschmann H (1983) Trans N Y Acad Sci Ser II 41 61-69 Hirschmann H, Hanson KR (1971a) Eur J Biochem 22 301-309 Hirschmann H, Hanson KR (1971b) J Org Chem 36 3293-3306... 

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