Stereoisomers categories

Isomerism is commonly encountered in covalent compounds but is rare among ionic compounds. Isomers can be grouped under two major categories, namely structural isomers and. stereoisomers [48, p. 45]. 

E/Z isomers (or cisitrans isomers) fall under this category. They are called diastereomers, because they are stereoisomers that are not mirror images of each other ... 

In order to effect the preferential formation of one stereoisomer (either enantiomer or diastereoisomer) over the other, either the reactant, or the reagent, or the solvent must be the pure enantiomeric form. Three principal categories may be recognised and they may be related to the illustrative examples noted above. 

The two categories into which stereoisomers can be placed are absolutely distinctive in definition. Two stereoisomers that are nonsuperimposable mirror images are called enantiomers. The only other category is defined negatively. Stereoisomers that are not enantiomers are called diastereomers. 

Stereoisomers that are not mirror images of one another are called diastereoisomers. Both of these pairs of isomers fall into this category. Notice how the physical and chemical properties of a pair of diastereoisomers differ. 

The geometry-based classification of stereoisomers, as discussed above, discriminates two mutually exclusive categories, namely enantiomers amd diastereoisomers. 

Catenanes, molecular knots, and other molecules in these structural categories can exist as enantiomers. In other words, stereoisomers can be generated in some cases. This phenomenon was first predicted by Frisch and Wassermann, and the... 

Distinguish between the two main categories of isomers, structural isomers and stereoisomers. 

Geometric isomers, a category of stereoisomers, result from different arrangements of groups about carbon atoms that are double bonded to each other. 

I explained this category in the case of the German cockroach pheromone (104), and also discussed the spined citrus bug pheromone [(3/ ,4S)-74], whose opposite enantiomer was as active as the pheromone itself. Females of the maritime pine scale Matsucoccusfeytaudi) use (3.S ,7R)-118 as the sex pheromone. Its OR,1R )-isomcr also showed bioactivity similar to the natural pheromone, while M. feytaudi males responded very weakly to the two other stereoisomers. It therefore seems that only the stereochemistry at C-7 of 118 is important for the expression of pheromone activity.139... 

The second major category of isomers and the focus of this chapter are stereoisomers. Being isomers they too have the same number and kind of building block atoms, but, unlike constitutional isomers, they have identical topologies. Stereoisomers, in turn, are divided into two groups enantiomers and diastereomers. Enantiomers are isomers that are not superimposable on their mirror images. And, by definition, diastereomers are all other stereoisomers that are not enantiomers. 

Coordination compounds often form isomers. Isomers are compounds with the same formula (or components) but different physical structures. There are two broad classes of isomers — constitutional, or structural isomers, and stereoisomers. Within these two categories, there are specific types of isomers, with different degrees of complexity. Figure 9-2 illustrates with a flowchart how the different types of isomers are related to one another. 

Stereoisomers fall into two categories, diastereoisomers and enantiomers. Diastereoisomers are stereoisomers that are not mirror-images of one another. Enantiomers are stereoisomers that are mirror-images of one another. In this section, we shall only be concerned with diastereoisomers. We return to enantiomers in Sections 4.8 and 20.8. 

Stereoisomers can be subdivided into two general categories those that are enantiomers of each other, and those that are diastereomers of each other. 

PROBLEM 5.22 Draw the two stereoisomers of 1,3-dimethylcyclobutane, and classify the pair according to the categories listed in A, B, and C above. 

A new category of stereoisomers is possible when a molecule contains more than one stereogenic center. In terms of absolute configuration, every stereo-genic center is treated as an independent unit and assigned the appropriate R or S absolute configuration. However, the presence of more than one stereogenic center poses new problems. 

Polymers based on lactic acid (PLA) are a most promising category of polymers made from renewable resources. They are not only compostable and biocompatible, but also pro-cessable with most standard processing equipment. The properties of lactic acid based polymers vary to a large extent depending on the ratio between, and the distribution of, the two stereoisomers or other comonomers [ 1-3]. The polymers can be manufactured by different polymerization routes, which are schematically described below (Figure 3.1). 

In Section 5.1, we saw that stereoisomers have the same constitution (connectivity of atoms) but are nonsuperimposable (they differ in their spatial arrangement of atoms). Stereoisomers can be subdivided into two categories, as shown in Figure 5.11. 

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