Two Types of Isomerism with Examples

This article throws light upon the two types of isomerism with examples. The types are: 1. Structural Isomerism 2. Stereo Isomerism. 

Structural Isomerism

Structural isomers the phenomenon as structural isomerism refers to isomers that differ solely in the arrangement of atoms or groups inside the molecule, without any reference to space. As a result, despite having differing structural formulae, the structural isomers have the same molecular formula.

i) Skeleton isomerism

This sort of isomerism is caused by the variation in the nature of the carbon chain (i.e., straight or branched) that forms the molecule’s nucleus. Example

two types of isomerism

ii) Position isomerism

It is due to a difference in the location of an atom or group in the side chain or an unsaturated link in the same carbon chain. Example

iii) Functional isomerism

This sort of isomerism is caused by differences in the types of functional groups present in the isomers, example

iv) Tautomerism

Tautomerism is the phenomena whereby a single chemical can exist in two readily interconvertible forms that differ significantly in the relative position of at least one atomic nucleus, often hydrogen. The two distinct structures are referred to as tautomers of one another. There are various varieties of tautomerism, the most significant of which being keto-enol tautomerism. One form (tautomer) of this type exists as a ketone and the other as an enol. The two most straightforward examples are acetone and phenol.

Stereo Isomerism

Stereoisomers and stereoisomerism are terms used to refer to isomers that have the same structural formula but differ in the relative arrangement of atoms or groups in space within the molecule. We can state that the stereoisomers have the same structural formula but a different configuration since the spatial arrangement of atoms or groups is also referred to as the molecule’s configuration.

i) Geometrical isomerism

Geometrical isomers and the phenomenon known as geometrical isomerism are isomers that share the same structural formula but differ in the spatial arrangement of the groups surrounding the double bond. The alkene family or their derivatives demonstrate this isomerism. Similar groups are on the same side in the cis isomer, however when they are on opposite sides, the isomer is called trans.

ii) Optical isomerism

This kind of isomerism results in two mirror images of each other when atoms or groups are arranged differently in space. The molecules of optical isomers have an asymmetric (chiral) carbon atom, which is bonded to four distinct atoms or groups. The only difference between optical isomers and other compounds is how they react to plane polarised light. Laevo (1) is the isomer that rotates plane polarised light to the left, whereas dextro is the isomer that rotates plane polarised light to the right (d).

For example: Enantiomers are d-and l -forms of a compound, which are non-super-imposable mirror image of each other. Racemic modification is an equimolecular mixture of d and l forms of the same compound. The process of converting d- or l- form of an optically active com­pound into dl- (racemic) form is known as racemisation.

Since the rotation of d is cancelled by equal but opposite rotation of l, racemic mixture (r) is always optically inactive. Separa­tion of dl-mixture of a compound into d and l isomers is known as resolution.