the-organic-chemistry

Definition of Stereoisomerism

Compounds/molecules that have some connectivity but different arrangements of atoms in space, so those compounds posses this situation is called stereoisomer and this phenomenon is said to be stereoisomerism.

OR

Stereoisomerism is caused by different arrangements of atoms or groups in Space.. This phenomenon is known as stereo isomerism.

Stereo=space
Isomerism=same molecular formula but differ in chemical/physical properties.

Stereoisomerism is exhibited by such compounds which have same structural formula but differ in configuration.

The term configuration refers to three dimensional arrangements of atoms, that characterize a particular compound.

Types of Stereoisomerism:

There are two types of stereo-isomerism:
1= Geometrical isomerism (cis-trans isomerism)
2= Optical isomerism

Geometrical Isomerism:

Those compounds having same molecular formula but a different geometric configuration as when atom or groups of atoms are attached in different special arrangements on either side of a bond or ring are said to be geometrical isomers and the phenomenon is known as geometrical isomerism.

Optical Isomerism:

It is a type of stereoisomerism, in which an optically active compounds can exist in two isomeric form which rotate plane-polarised light in opposite direction. These are called optical isomers and phenomenon is said to be optical isomerism.

Type of functional isomerism in which the isomers are in dynamic equilibrium with each other. commonly they are also called as Keto or Enol form

keto= ketone group
enol= alcohol group

So the process in which keto form is converted to enol form is said to be Tautomerization. this interconversion takes place by the movement of hydrogen.

1. Acetone Tautomerization

2. Tautomerization in Lactam-Lactim

Explanation:

When writing the resonance structures of a compound. It was observed that the relative position of atomic nuclei remained unchanged. The structures which differ in the relative position of their atoms are not resonance form but different compounds which are isomeric with each other and are capable independent existence. The most common example of Tautomerism are provided buy carbonyl compounds containing alpha-hydrogen, in which the proton (hydrogen) from alpha-carbon shifts to carbonyl oxygen, associated with appropriate movement of electron pair form an ENOL , this process is called ENOLIZATION. The hydrogen then moves back to convert the enol form to keto form.





Keto form is therefore more stable by 69kj/mol. 

HISTORY:

Isomerism:

• Chain Isomerism
• Position Isomerism
• Functional Isomerism
• Metamerism Isomerism
• Tautomerism                                    

Constitutional  Isomerism or structural isomers is shown by the compounds that have the same molecular formula but different connectivity.

1. Chain Isomerism:

2. Position Isomerism: