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1 Some Basic Concepts of Chemistry 2 Structure of Atom 3 Classification of Elements and Periodicity in Properties 4 Chemical Bonding and Molecular Structure 5 Thermodynamics 6 Equilibrium 7 Redox Reactions 8 Organic Chemistry – Some Basic Principles and Techniques 9 Hydrocarbons

8 Organic Chemistry – Some Basic Principles and Techniques

8.1 General Introduction (Organic Chemistry) 8.2 Tetravalence of Carbon - Shapes of Organic Compounds 8.3 Structural Representations of Organic Compounds 8.4 Classification of Organic Compounds 8.5 Nomenclature of Organic Compounds 8.6 Isomerism 8.7 Fundamental Concepts in Organic Reaction Mechanism 8.8 Methods of Purification of Organic Compounds 8.9 Qualitative Analysis of Organic Compounds 8.10 Quantitative Analysis of Organic Compounds

Classification of Organic Compounds

NCERT Reference:Chapter 8 – Organic Chemistry – Page 255–257 (Part II)

Quick Notes

  • Acyclic Compounds: Open-chain structures, saturated or unsaturated.
  • Cyclic Compounds: Closed rings, either carbocyclic (all carbon) or heterocyclic (with other atoms).
  • Aromatic vs Aliphatic: Aromatic compounds have delocalized π-electrons in rings; aliphatic do not.
  • Functional Group: A specific group of atoms responsible for chemical properties (e.g., –OH, –COOH).
  • Homologous Series: Series of compounds with the same functional group differing by –CH2–.

Full Notes

Due to the vast and growing number of organic compounds, it is essential to classify them based on structure. Organic compounds are broadly classified into:

Acyclic or Open-Chain Compounds

These compounds have straight or branched chains and are also called aliphatic compounds.

Examples:

NCERT 11 Chemistry acyclic open-chain examples showing ethanol CH3CH2OH, ethanal CH3CHO, and 2-methylpropane CH3CH(CH3)CH3.

Cyclic or Closed Chain / Ring Compounds

These contain atoms joined to form rings. Two major types:

Alicyclic Compounds

Aliphatic cyclic compounds: made of rings formed by carbon atoms.

NCERT 11 Chemistry alicyclic ring examples including cyclobutane, cyclohexane and cyclohexene.

Heterocyclic Compounds

These rings also contain atoms other than carbon (like O, N, S).

NCERT 11 Chemistry heterocyclic ring examples such as tetrahydrofuran with oxygen in the ring and piperidine with nitrogen in the ring.

Aromatic Compounds

Special ring compounds with delocalized electrons.

Include benzene and related structures.

May also be heterocyclic (contain non-carbon atoms in ring).

Benzenoid Aromatic Compounds: Based on benzene ring

NCERT 11 Chemistry benzenoid aromatic examples including benzene, aniline and naphthalene with delocalised pi electrons.

Non-Benzenoid Aromatic Compounds: Do not contain benzene ring

NCERT 11 Chemistry non-benzenoid aromatic examples such as tropone and azulene that are aromatic without a benzene ring.

Heterocyclic Aromatic Compounds: Ring contains atoms like N, O, or S

NCERT 11 Chemistry heterocyclic aromatic examples including furan with oxygen, thiophene with sulfur and pyridine with nitrogen in the ring.

Organic compounds can also be classified by functional groups into families or homologous series.

Functional Group

A functional group is an atom or group of atoms bonded to a carbon chain that determines the characteristic chemical properties of an organic compound.

NCERT 11 Chemistry functional groups overview showing common groups such as hydroxyl, carbonyl, carboxyl, amino and halo.

Homologous Series

A homologous series is a group of organic compounds with the same functional group and general formula, differing by a –CH2– unit between successive members.

Members of the series are called homologues.

Each series shares similar chemical properties but gradual changes in physical properties.

Examples of homologous series (see table above in 8.4.1):

Compounds can also contain more than one functional group, these are called a polyfunctional compounds.

Summary