Stereoisomerism optical isomerism

Some alkenes can also have cis and trans isomers, one of two forms of stereoisomerism. Here the homers have the same molecular formulas and the same atom-to-atom bonding sequences, but the atoms differ in their arrangement in space. The other form of stereoisomerism, optical isomerism, is discussed in Section 15.1. 

In stereoisomers, the number and types of atoms and bonds in molecules are the same, but certain atoms are oriented differently in space. Cis and trans isomerism is one type of stereoisomerism optical isomerism is another. 

The second type of stereoisomerism is optical isomerism, in which two molecules that are mirror images of each other are not superimposable on each other. Consider the compound 2-butanol, CH3CH(OH)CH2CH3. It has two optical isomers, because it is not superimposable on its mirror image. 

You have already covered structural isomerism in earlier work and we will now explore stereoisomerism. There are two types of stereoisomerism geometric isomerism and optical isomerism. 

Linear macromolecules having a constitutional repeating unit such as -CH2-CHX- (X H) show two further stereoisomerisms, i.e., optical isomerism and tacticity. The stereoisomerism named tacticity has its origin in the different spatial arrangements of the substituents X. When we arrange the carbon atoms of the polymer main chain in a planar zigzag conformation in the paper plane. 

In stereoisomerism, three dimensions must be considered. In stereoisomerism (also termed optical isomerism), there is no plane of symmetry in the molecule, so that the two forms are mirror-images, and thus cannot be turned into a position of coincidence. Thus, compounds containing a carbon atom (or other tetravalent atom) to which four different atoms or radicals are bonded are optical isomers. They receive this name from the fact that one isomer rotates the plane of polarized light to the right (d extra form) the other rotates it to the left (leva form). Lactic acid is an example. See also Lactic Acid, and formulas below ... 

Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer (atoms are connected in the same sequence). The two main types of stereoisomerism are cis-trans or Z-E isomerism and optical isomerism. 

Stereoisomerism occurs in vinyl polymers when one of the carbon atoms of the monomer double bond carries two different substituents. It is formally similar to the optical isomerism of organic chemistry in which the presence of an asymmetric carbon atom produces two isomers which are not superimposable. Thus glyceraldehyde exists as two stereoisomers with configurations shown in 4-13. (The dotted lines denote bonds below and the wedge signifies bonds above the plane of the page.) Similarly, polymerization of a monomer with structure... 

Chemical compounds that have the same molecular formula but different structural formulas are said to be isomers of each other. These constitutional isomers (or structural isomers) differ in their bonding sequence, i.e. their atoms are connected to each other in different ways. Stereoisomers have the same bonding sequence, but they differ in the orientation of their atoms in space. Stereoisomerism can be further divided into optical isomerism (enantiomerism) and geometrical isomerism (cis—trans isomerism). The relationships between the different types of isomerism are shown in Figure 4.1. 

These concepts are difficult for many people to fully grasp unless they use molecular models. This form of stereoisomerism is known as optical isomerism because chiral molecules have unique effects on polarized light. Molecules containing all carbon atoms with three or fewer different entities attached cannot be enantiomers and are called achiral. 

Optical isomerism is a form of isomerism (specifically stereoisomerism) where the two different isomers are the same in every way except being non-superposable mirror images of each other. Optical isomers are known as chiral molecules (pronounced ki-rall). 

Fig. 2.2 Examples of stereoisomerism (a) optical isomerism involving acyclic and cyclic carbon atoms (indicates stereogenic centre) (b) cis and trans diastereomers in unsaturated compounds (R and R = aliphatic or aromatic groups).

Optical Activity in Polymers Stereoisomerism in polymers is formally similar to the optical isomerism of organic chemistry. In a vinyl polymer with the general structure shown in (XIH) every other carbon atom in the chain, labeled C, is a site of steric isomerism, because it has four different substituents, namely, X, Y, and two sections of the main chain that differ in length (Rudin, 1982). 

Another type of stereoisomerism Is optical Isomerism, which we will meet later. 

A second type of stereoisomerism is called optical isomerism because the isomers have opposite effects on plane-polarized Ught. When Ught is emitted from a source such as a glowing filament, the oscillating electric fields of the... 

Carbon, far more than any other atom, is responsible for the principal forms of stereoisomerism dealt with in this and the following two sections. Most of the examples of optical isomerism arise from the presence in the molecule of a carbon atom with four single bonds, each of which is connected to a different kind of atom or group. Such a carbon atom, i.e. one with four different kinds of substituents, is called asymmetric. 

The second type of stereoisomerism listed in Figure 23.19 is optical isomerism. Optical isomers, called enantiomers, are mirror images that cannot be superimposed on each other. They bear the same resemblance to each other that your left hand bears to your right hand. If you look at your left hand in a mirror, the image is identical to your right hand ( Figure 23.22). No matter how hard you try, however, you cannot... 

Tacticity in macromolecules arises because ordered monomeric units possess the elements of either geometrical or optical isomerism. If two elements of stereoisomerism are present in a unit and the monomer unit is ordered with respect to both elements, the polymer is said to possess ditacticity. 

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