Stereoisomerism geometrical isomers

This rotational restriction leads to another type of stereoisomerism. Geometric isomers (also called cis-trans isomers) have different orientations of groups around a double bond (or similar structural feature). Table 15.4 shows the two geometric isomers of 2-butene (also see Comment, Sample Problem... 

This rotational restriction leads to another type of stereoisomerism. Geometric isomers (also called cis-trans isomers) have different orientations of groups around... 

Stereoisomeric alkenes are sometimes referred to as geometric isomers... 

Although they are built from the same numbers and kinds of atoms, structural isomers have different chemical formulas, because the formulas show how the atoms are grouped in or outside the coordination sphere. Stereoisomers, on the other hand, have the same formulas, because their atoms have the same partners in the coordination spheres only the spatial arrangement of the ligands differs. There are two types of stereoisomerism, geometrical and optical. 

Pyrethroids have two kinds of stereoisomerism, i.e., geometric isomerism and enantiom-erism. The cyclopropene ring shown in the general structure acts like a double bond, resulting in geometric isomers, cis/trans or Z/E forms, depending on whether the two substitutes (C-l and C-3) are on the same side (cis or Z) or on opposite sides (trans or E), as shown in the following text ... 

Stereoisomerism manifests itself in various forms, such as those related to enantiomers, epimers, diastereoisomers, meso compounds, geometrical isomers, etc. Generally speaking, the consequences of stereoisomerism for the disposition and biological action of xenobiotics in living... 

The sp hybridized carbon atoms of alkenes (olefins) and the atoms or groups attached to these carbons all lie in the same plane, and rotation around the double bond is restricted. As a result, stereoisomerism is possible when each carbon atom of the double bond is asymmetrically substituted. Because geometric isomers are non-superimposable, non-mirror images they... 

One of the earliest cases of stereoisomerism among inner complexes, tris(glycinato)cobalt(III), occurs in two forms, violet (a) and red (P). In one of these geometric isomers, all of the amino groups of the glycine molecules are adjacent (fac), while in the other, two of these occupy opposite positions mer). Absorption spectra indicate that the more soluble violet a form is the mer isomer. " ... 

The reactant, too, exists as diastereomers a pair of geometric isomers. If we start with, say, ci5-2-butene, which of the stereoisomeric products do we get A mixture of all of them No. cw-2-Butene yields only racemic 2,3-dibromobutane none of the meso compound is obtained. A reaction that yields predominantly one stereoisomer (or one pair of enantiomers) of several diastereomeric possibilities is called a stereoselective reaction. 

According to lUPAC the term geometric isomerism" is an obsolete synonym of cis-trans isomerism and its use is strongly discouraged. Sometimes the term geometric isomerism has been used as a synonym of stereoisomerism, i.e. optical isomers being considered to be geometric isomers. This, however, is not consistent with current standard chemical nomenclature. The exact term for stereoisomers that are not optical isomers is diastereomers. 

Characteristically, metal ions form complexes that can exist as several isomers. This is a consequence of the stereochemistry, resulting from high numbers of ligands, adopted by most metal complexes. The best known examples of isomerism in complexes are geometrical isomers (such as cis and trans isomers), but these are not the sole type. We can, following a traditional approach, divide the area into two classes constitutional (or structural) isomerism and stereoisomerism. 

In stereoisomerism all atoms in the compounds are attached to the same partners, but the partners are arranged differently in space. Geometric isomerism, the isomerism shown by some alkenes because there is no free rotation about the double bond, is one type of isomerism in this class. The geometric isomers of 1,2-dichloroethene are shown below ... 

In addition to geometry, alkenes also differ from open-chain alkanes in that the double bonds prevent the relatively free rotation that is characteristic of carbon atoms bonded by single bonds. As a result, alkenes can exhibit geometric isomerism, the same type of stereoisomerism seen earlier for the cycloalkanes (Section 1.9). There are two geometric isomers of 2-butene ... 

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