Isomerism

Isomerism

What is Isomerism?

Isomerism is the phenomenon where two or more molecules have the same molecular formula but different structures, resulting in different physical and chemical properties. Isomers are molecules that have the same number of atoms and the same types of bonds between them but differ in the spatial arrangement of their atoms.

Isomerism is an important concept in chemistry because it has a significant impact on the physical and chemical properties of molecules. For example, two isomers may have different melting points, boiling points, solubilities, and reactivities.

Types of Isomerism

There are different types of isomerism, including structural isomerism, stereoisomerism, and tautomeric isomerism. Let’s explore each type in more detail:

1. Structural isomerism: This occurs when two or more molecules have the same molecular formula but different structural arrangements of their atoms. In other words, their atoms are arranged in different ways. For example, the compounds butane and isobutane have the same molecular formula (C4H10) but different structural formulas, as shown below:Butane: CH3CH2CH2CH3 Isobutane: (CH3)3CH
2. Stereoisomerism: This occurs when two or more molecules have the same molecular formula and the same structural formula but differ in their spatial arrangement. In other words, the atoms are arranged in the same order, but they are oriented differently in space. There are two types of stereoisomers:a. Geometric isomerism: This occurs when two or more molecules have the same molecular formula and the same structural formula, but differ in the orientation of groups around a double bond or a ring. For example, cis- and trans- isomers of but-2-ene:b. Optical isomerism: This occurs when two or more molecules have the same molecular formula and the same structural formula, but are mirror images of each other and cannot be superimposed on each other. These molecules are called enantiomers. Enantiomers have identical physical and chemical properties, except for their interaction with polarized light. One enantiomer rotates the plane of polarized light to the right (dextrorotatory or +), while the other rotates it to the left (levorotatory or -). An example of a pair of enantiomers is the amino acid alanine.
3. Tautomeric isomerism: This occurs when two or more molecules can exist in two forms that are rapidly interconverted by a chemical reaction, such as a shift of a hydrogen atom or a double bond. Tautomeric isomers have different chemical properties and often exhibit different reactivities. For example, the keto-enol tautomerism in the molecule acetone:Ketone form: CH3COCH3 Enol form: CH2=CHOHCH3

Examples of each type of isomerism:

1. Structural isomerism:
   • Butane (CH3CH2CH2CH3) and Isobutane ((CH3)3CH) are structural isomers of each other.
2. Geometric isomerism:
   • Cis- and trans- isomers of but-2-ene (CH3CH=CHCH3) are geometric isomers of each other.
   • Cis- and trans- isomers of cyclohexane-1,2-dicarboxylic acid (HOOC(CH2)4COOH) are geometric isomers of each other.
3. Optical isomerism:
   • L-alanine and D-alanine are enantiomers of each other.
   • L-glucose and D-glucose are enantiomers of each other.
4. Tautomeric isomerism:
   • Keto and enol forms of acetone (CH3COCH3) are tautomers of each other.
   • The keto and enol forms of tautomerism in nucleic acid bases such as adenine and thymine.

First Year Pharm D Subjects Syllabus, Notes, PDF Books, MCQ

1.1	Human Anatomy and Physiology
1.2	Pharmaceutics
1.3	Medicinal  Biochemistry
1.4	Pharmaceutical Organic Chemistry
1.5	Pharmaceutical Inorganic Chemistry
1.6	Remedial Mathematics/ Biology

Suggested readings:

• 401T Pharmaceutical Organic Chemistry III Theory Notes, PDF Books
• Levels of structural organization and body systems
• Structural and functional classification of Joints
• General principles of cell communication
• 808ET Cell and Molecular Biology Theory Notes, PDF Books, MCQ