Organic compounds stereoisomerism

In the previous chapters, we discussed electron distrihution in organic molecules. In this chapter, we discuss the three-dimensional stracture of organic compounds. The structure may be such that stereoisomerism is possible. Stereoisomers are compounds made up of the same atoms bonded by the same sequence of bonds but having different three-dimensional stracmres which are not interchangeable. These three-dimensional structures are called configurations. 

Schultz, H. P., Schultz, E. B., Schultz, T. P. Topological organic chemistry. 9. Graph theory and molecular topological indices of stereoisomeric organic compounds. J. Chem. Inf. Comput. Sci. 1995, 35, 864-870. 

Schultz, H.P., Schultz, E.B. and Schultz, T.P. (1995). Topological Organic Chemistry. 9. Graph Theory and Molecular Topological Indices of Stereoisomeric Organic Compounds. J.Chem. Inf.Comput.ScL, 35, 864-870. 

Can recognise stereoisomerism (geometric and optical) in organic compounds. 

Stereoisomerism Ster-e-o- l-s9-m9r [ISV] (1894) n. A kind of isomerism in organic compounds arising from the fact that a carbon atom hnked to four different groups can exist in two spatially different forms that, though chemically identical, are not superimposable. A simple example is lactic acid, CHaCHCOH-COOH). 

Databases such as the NIST Mass Spectral Library (107,216 organic compounds, 5,943 duplicates or stereoisomeric pairs detected in the 1998 version) or the Maybridge Combinatorial Chemistry Database (MayDec02CCeus, 13,410 compounds with 19 duplicates) were processed by MOLGEN-CID. 

As well as stereoisomerism and geometrical isomerism, polymers and copolymers can exhibit a third form of isomerism regioisomerism. Head-to-head, head-to-tail and tail-to-head isomerism is well known for simple organic compounds. Thus, a dimer of styrene monomer can exist in the following three different regioisometric forms ... 

In the final analysis, SnI reactions, unlike Sn2 processes, are of limited use in synthesis because they fail the first two criteria of green reactions (see Real Life 3-1) They are poor in atom efficiency and wasteful overall, because they tend to lead to mixtures of stereoisomeric substitution products as well as other organic compounds. Sn2 is greener. ... 

The first observation of the effect of stereoisomerism on kinetics in the electrochemical reduction of organic compounds was made in 1928 by Herasymenko [2], who found a difference in the behavior of maleic and fumaric acids at the dropping mercury electrode. This pair of geometrical isomers, which are distinguished by fairly rigidly fixed orientation ... 

Stereoisomerism in Organic Compounds 26-8 From Molecular Formula to Molecular Structure... 

The second type of stereoisomerism encompasses all other cases in which the three-dimensional structures of two isomers exhibiting the same connectivity among the atoms are not superimposable. Such stereoisomers are referred to as diastereomers. Diastereomers may arise due to different structural factors. One possibility is the presence of more than one chiral moiety. For example, many natural products contain 2 to 10 asymmetric centers per molecule, and molecules of compound classes such as polysaccharides and proteins contain hundreds. Thus, organisms may build large molecules that exhibit highly stereoselective sites, which are important for many biochemical reactions including the transformation of organic pollutants. 

Factors which influence the stereoselectivity of organic reactions have been under intense investigation recently because of the increasing requirement and profitability of producing stereoisomerically pure compounds. A great deal of progress has been made, but even more remains to be accomplished. The specific contributors to stereoselectivity in individual reactions will be discussed as they are encountered. At this point it is important to be aware of the stereochemical variations that are possible. 

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