Unit 1: Classification, Nomenclature and Isomerism

February 20, 2026

Semester 2
BP202T

Introduction to Classification, Nomenclature and Isomerism

Unit 1 lays the foundation for all of Organic Chemistry. You must master how organic compounds are classified (Open chain / Cyclic), named systematically using IUPAC rules, and how the same molecular formula can represent different structures (Isomerism). These concepts are tested regularly and are essential for the rest of the course.
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Syllabus & Topics

  • 1Classification of Organic Compounds: Open chain (Aliphatic) and Closed chain (Cyclic – Carbocyclic and Heterocyclic).
  • 2Common system of nomenclature vs IUPAC system of nomenclature.
  • 3IUPAC rules for naming organic compounds up to 10 Carbons (open chain and carbocyclic compounds).
  • 4Structural Isomerism: Definition and types.
  • 5Chain Isomerism: Variation in carbon skeleton.
  • 6Position Isomerism: Difference in position of substituents or functional groups.
  • 7Functional Group Isomerism: Same formula but different functional groups.
  • 8Metamerism: Same functional group but different alkyl groups on either side.
  • 9Tautomerism: Dynamic equilibrium between two interchangeable structures.

Learning Objectives

Apply IUPAC Rules: Name any given simple organic compound correctly.
Classify Compounds: Identify whether a compound is aliphatic, carbocyclic, or heterocyclic.
Identify Isomers: Given a molecular formula, draw all possible structural isomers.
Explain Tautomerism: Illustrate the keto-enol tautomerism in acetaldehyde.
Distinguish by Nomenclature: Tell the difference between common and IUPAC names for the same compound.

Frequently Asked Questions (FAQs)

Q1. What is the first step in naming a compound by IUPAC?

The first step in IUPAC nomenclature is to identify the longest continuous carbon chain (parent chain). Then, determine the principal functional group and number the carbon atoms to give it the lowest possible locant.

Q2. What is the difference between Chain and Position Isomerism?

  • Chain isomerism: The carbon skeleton differs (different branching pattern).

  • Position isomerism: The carbon skeleton is the same, but the position of a functional group or substituent changes.

Q3. What is Tautomerism?

Tautomerism is a type of structural isomerism in which two forms exist in dynamic equilibrium. The most common example is keto–enol tautomerism in carbonyl compounds.

Q4. What is a Heterocyclic compound?

A heterocyclic compound is a cyclic compound in which at least one atom in the ring is not carbon, such as pyridine, which contains a nitrogen atom in the ring.

Q5. How many carbon atoms per chain are covered under IUPAC nomenclature in B.Pharm?

In the B.Pharm syllabus (BP202T), IUPAC nomenclature is generally covered for open-chain and carbocyclic compounds containing up to 10 carbon atoms.