Discuss the concept of isomerism in organic com... - SS2 Chemistry Organic Chemistry I: Hydrocarbons Question

Isomerism refers to the phenomenon where compounds have the same molecular formula but differ in their arrangement or connectivity of atoms. Isomers exhibit distinct chemical and physical properties due to their structural differences. In organic chemistry, three main types of isomerism are observed:

1.    Structural Isomerism: Structural isomers have the same molecular formula but differ in the arrangement of atoms within the molecule. This can occur due to different carbon skeleton arrangements, functional group positions, or bond connectivity. Examples include:

●     Butane (C4H10) and 2-methylpropane (C4H10): Both compounds have the molecular formula C4H10, but butane has a straight-chain structure, while 2-methylpropane has a branched structure.

●     Ethanol (C2H5OH) and dimethyl ether (C2H6O): Both compounds have the same molecular formula, but ethanol has an -OH functional group, whereas dimethyl ether has an -O- functional group.

2.    Stereoisomerism: Stereoisomerism arises from the different spatial arrangements of atoms in a molecule, resulting in compounds with identical connectivity but differing in their three-dimensional orientation. There are two types of stereoisomerism:

●     Geometric Isomerism (Cis-trans isomerism): It occurs in compounds with restricted rotation around a double bond or a ring structure. In cis-trans isomerism, the groups on either side of the double bond or ring can be arranged differently. Examples include cis- and trans- isomers of 2-butene.

●     Optical Isomerism (Enantiomerism): Optical isomers, also known as enantiomers, are non-superimposable mirror images of each other. They have a chiral centre, which is a carbon atom bonded to four different groups. Enantiomers have identical connectivity but differ in their spatial arrangement. An example is D-glucose and L-glucose.

3.    Functional Group Isomerism: Functional group isomers have the same molecular formula, but different functional groups are present in the molecule. Examples include:

●     Propanal (C3H6O) and acetone (C3H6O): Both compounds have the same molecular formula, but propanal contains an aldehyde functional group (-CHO), while acetone contains a ketone functional group (-C=O-).