Stereochemistry is defined as a subdiscipline of chemistry which involves the study of the relative spatial arrangement of atoms that together forms the structure of molecules and their manipulation. The study of chiral molecules which is one of the elements of symmetry is an important branch of stereochemistry.
In other words, stereochemistry belongs to that department of chemistry which take care of the three-dimensional structures of molecules and how they are an impact on the chemical and the physical properties of the substance.
Let’s look at a few points to note on Stereoisomerism.
- Stereoisomerism refers to isomerism which is caused due to non-similar arrangements of the molecules, atoms or groups in space.
- The isomers of stereoisomers have the same constitution although the spatial arrangements of their atoms are very different.
There are two types of stereoisomers.They are known as enantiomers and diastereomers.
The mirror images which are also non-superimposable isomers are known as the Enantiomers and the isomerism which are exhibited by the same are known as Enantiomerism. There is another type of Isomerism which does not behave as the mirror image of each other. They are the diastereomers.
Enantiomers are stable and isolable compounds that differ from each other in the spatial arrangements of the three-dimensional area and mostly exist as discrete pairs.
The properties of enantiomers are identical although their interaction with a plane of polarized light varies. They exhibit similar melting point, color, and reactivity with acids and bases, solubility and density. However, the direction in which they rotate the plane polarized light is different, that is, if one rotates in right direction, the other rotates towards the left.
In diastereomers, all the asymmetrically arranged carbon atom present increases to twice the number of theoretically possible isomers. Therefore, a molecule which has an ‘n’ number of asymmetric carbon atoms would end up having 2n stereoisomers.
You can notice that in the first image, (i) is, the mirror image of (ii), and in the second image, (iii) is the mirror image of (iv). Therefore, the total four isomers form from the two pairs of enantiomers. When (i) and (iii) are compared, they are neither superimposable nor mirror images hence they are termed as diastereomers.
Stereochemistry of syn-addition
In Syn-addition, the groups inclusive of the reacting molecules are added in same faces to that of the molecule. These type of addition reactions are stereospecific additions.
When we observe a maleic Hydrogenation acid by using Wilkinson’s catalyst the structure which is formed is as below.
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