Introduction to Stereoisomerism

In the previous section, we reviewed cis-tram stereoisomerism, but there are many other kinds of stereoisomers. We begin our exploration of the various kinds of stereoisomers by investigating the relationship between an object and its mirror image. 

Objects, like hands, that are not superimposable on their mirror images are called chiral objects, from the Greek word cheir (meaning hand ). All three-dimensional objects can be classified as either chiral or achiral. Molecules are three-dimensional objects and can therefore also be classified into one of these two categories. Chiral molecules are like hands they are nonsuperimposable on their mirror images. Achiral molecules are not like hands they are superimposable on their mirror images. What makes a molecule chiral  

For other sources of molecular chirality, see the Challenge Problems at the end of this chapter. 

There are two ways to arrange four different groups around a carbon atom. 

To see that these two compounds are nonsuperimposable, build a molecular model using any one of the commercially available molecular model kits. 

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The discussion of rotamers is taken in part from Silverstein, R.M., and LaLonde, R.T. (1980)./. Chem. Educ., 57,343 t For excellent introductions to stereoisomeric relationships of groups in molecules, see Mislow, K., and Raban, M. (1967). In Topics in Stereochemistry, Vol. I. page 1 Jennings, W.B. (1975) Chem. Rev., 75, 307. These authors prefer the term spin-coupling equivalence. ... 

Arrow Pushing and Carbocation Introduction to Stereoisomerism (Section 5.2)... 

Mislow, K. 1965. Introduction to Stereochemistry. Reading, Mass., Benjamin/Cummings. Mislow, K., and M. Raban. 1967. Stereoisomeric Relationships of Groups in Molecules, in Topics in Stereochemistry, Allinger, N. L., and Eliel, E. L., eds. Vol. 1, 1-38. New York Interscience. 

Free MI undergoes phosphorylation by a Mg2+-activated, ATP-dependent MI kinase (MIK, EC 2.7.1.64) to yield MI-1 -P of the same stereoisomeric form produced by MIPS (English et al., 1966 Loewus, M.W. et al., 1982). For an introduction to current recommendations on rules for numbering atoms in wvo-inositol see http //www.chem.qmul.ac.uk/iupac/cyclitoFmyo.html. 

In order to depart to the third dimension to perform asymmetric synthesis in a way to obtain only or prevalently one enantiomer of the target molecule, there is a substantial prerequisite chiral information has to be present in the reaction system. This is materialized as a chiral catalyst, chiral auxiliary agent or even chiral solvent. Detailed discussion of stereoisomerism as an introduction to stereoselective reactions is presented in Chap. 3. We suggest detailed study of the following examples after reading this chapter. 

Basic introduction to organic structures, including stereoisomerism. 

This concludes an introduction to the IR spectra of polymers. Clearly, the interpretation of polymer spectra can be reasonably straightforward based on the group frequency logic that has been developed to deal with relatively small organic molecules. There are, however, complexities which result from the fact that these solid systems may be associated with configurational isomerism, stereoisomerism, and conformational isomerism. These added complexities affect the spectra and must be remembered and taken into account in the interpretive process. Finally, there are aids such as the flow... 

He himself found that aldonolactones could be reduced with sodium amalgam to the aldoses. Thus, the way was opened to proceed from any pentose to the next higher aldose, which, as he soon showed, always arose in two stereoisomeric forms because of the introduction of a new asymmetric center. Another novel method created was the epimerization of aldonic... 

Many convenient methods for the introduction of carbon-carbon double bonds into a saturated carbon chain involve the removal of two atoms or groups from adjacent carbon atoms. Usually, but not invariably, one of these groups is hydrogen (i.e. the removal of HX). Two main types of elimination reactions are recognised - heterolytic processes in solution and pyrolytic reactions in the gas phase. A detailed discussion of the mechanisms of these reactions may be found in all standard and advanced textbooks in each of the reactions discussed below the probable mechanism is noted in relation to the aim of obtaining good yields of regio- or stereoisomerically pure compounds. 

Evidence for the S pentadienyl ions has been obtained from kinetic and stereochemical studies on the solvolysis of dinitrobenzoate esters of dia-stereoisomeric alcohols like 22 and 23. An SN1 mechanism is suggested for the solvolyses, which proceed essentially with retention of configuration at C-l, (162-164,167). S-Shaped ions have also been observed directly by low-temperature NMR studies of the protonation of suitable alcohols. The normally rapid rearrangement of the S ion to the U ion is inhibited to some extent by destabilizing the U ion by introduction of an anti substituent (168) [Eq. (18)] or by constraining the S structure partly in a ring system (169). The... 

The purpose of the present paper is to review this field of research - a summary of this review appeared in (4). After a brief introduction (part 2) to the XPS technique itself, specially oriented to the study of the polymer valence bands, given in order to stress upon the inherent difficulties (and limitations) of the experiment, we shall present specific examples of the various types of informations that can be acquired on the polymer molecular and electronic structure (part 3) substitution effects in the valence bands (part 4) structural isomerism, stereoisomerism, and geometrical crystalline structure (part 5) other types of information. 

Alder route, was converted into the urethan (25) by a series of unexceptional steps. Arndt-Eistert homologation of (25) provided the carboxylic acid (26) which, upon treatment with acetic anhydride, readily gave the lactam (27). Introduction of a one-carbon unit into the aromatic ring was achieved with chloromethyl methyl ether, and further reductive and hydrolytic modification afforded the amino-alcohol (28). Osmium tetroxide oxidation of (28) yielded the stereoisomeric triols (29) (20%) and (30) (22%) which were separated and oxidized to ( + )-clivonine (31) and (+ )-clividine (32), respectively. 

Diastereomers were defined in the Introduction as stereoisomers that are not related as an object and its mirror image. Consider the four structures in Fig. 2.1. These structures exemplify the four possible combinations of two nonequivalent chiral centers in the stereoisomers of 2,3,4-trihydroxybutanal. The configurations at C-2 and C-3 are indicated according to the Cahn-Ingold-Prelog convention. Each structure is stereoisomeric with respect to any of the others. The 2R,3R and 2S,35 isomers are enantiomeric, as is the 25,3/ and 2R,3S pair. The 2R,3R isomer is diastereomeric with respect to the 2R,3S isomer, since they are stereoisomers but not enantiomers. The mirror image of 2R,3R is 25,35, and any object can have only one mirror image. 

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