Define isomerism and explain the different type... - SS1 Chemistry Organic Chemistry Question

Isomerism refers to the phenomenon in which two or more compounds have the same molecular formula but differ in their structural arrangement or spatial orientation, resulting in distinct chemical and physical properties. Isomers have the same number and types of atoms but differ in their connectivity or arrangement of atoms within the molecule.

 

The different types of isomerism observed in organic compounds include:

 

1. Structural Isomerism: Structural isomers, also known as constitutional isomers, have the same molecular formula but differ in the connectivity of atoms. Examples of structural isomers include:

-       Chain isomerism: In chain isomerism, the carbon chain is arranged differently. For example, pentane and 2-methylbutane both have the molecular formula C₅H₁₂ but differ in the arrangement of their carbon chains.

-       Position isomerism: Position isomers have the same carbon skeleton, but the functional group or substituent is attached at different positions. An example is 1-propanol and 2-propanol, which both have the molecular formula C₃H₈O but differ in the position of the hydroxyl group.

 

1. Stereoisomerism: Stereoisomers have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of atoms within the molecule. Stereoisomerism can be further classified into two types:

-       Geometric isomerism: Geometric isomers have restricted rotation around a bond, leading to different spatial arrangements. The most common form of geometric isomerism is cis-trans isomerism. For example, in cis-2-butene and trans-2-butene, the carbon-carbon double bond is fixed, resulting in different spatial arrangements of the substituents.

-       Optical isomerism: Optical isomers, also known as enantiomers, are non-superimposable mirror images of each other. They have a chiral centre, which is an atom attached to four different groups. Enantiomers exhibit optical activity, rotating the plane of polarised light in opposite directions. An example is D-glucose and L-glucose, which have the same molecular formula (C₆H₁₂O₆) but differ in their spatial arrangement around the chiral carbon.

 

1. Tautomeric Isomerism: Tautomers are isomers that exist in equilibrium with each other through the migration of a proton. They interconvert rapidly, and the equilibrium is influenced by conditions such as temperature and pH. An example is the keto-enol tautomerism in compounds such as acetone and enol form, where the position of a hydrogen atom and double bond switch.