This lesson introduces the foundations of organic chemistry, including structure, bonding, functional groups, nomenclature, and isomerism. It prepares students for understanding more complex organic reactions.

1. Core Concepts (Short Notes)

11.1 What Is Organic Chemistry?

Organic chemistry is the study of carbon-containing compounds, especially those involving carbon–hydrogen bonds.

• Carbon forms strong covalent bonds.

• Can form long chains and rings.

This versatility makes organic chemistry one of the largest branches of chemistry.

11.2 Structure of Organic Molecules

Organic molecules can be represented using:

• Molecular formula: Shows total number of atoms (e.g., C₂H₆O).

• Structural formula: Shows arrangement of atoms.

• Displayed formula: Shows every bond.

• Condensed formula: CH₃CH₂OH.

11.3 Functional Groups

Functional groups determine the chemical behavior of organic compounds. Examples:

• Alcohol (–OH)

• Aldehyde (–CHO)

• Ketone (>C=O)

• Carboxylic acid (–COOH)

• Amine (–NH₂)

• Alkene (C=C)

Functional groups allow classification of organic compounds.

11.4 Homologous Series

A series of compounds with:

• Same functional group.

• Same general formula.

• Similar chemical properties.

• Gradual change in physical properties.

Example: Alkanes → CₙH₂ₙ₊₂.

11.5 Saturated vs. Unsaturated Compounds

• Saturated: Only single carbon–carbon bonds (alkanes).

• Unsaturated: Contains double or triple bonds (alkenes, alkynes).

11.6 Aromatic Compounds

Contain delocalized π-electrons in a ring.

• Example: benzene (C₆H₆).

• Undergo substitution rather than addition.

11.7 Types of Bonding in Organic Molecules

• Sigma (σ) bonds: Strong single bonds.

• Pi (π) bonds: Weaker, present in double and triple bonds.

11.8 Isomerism

Compounds with the same molecular formula but different structures.

Structural Isomerism:

• Chain isomers

• Position isomers

• Functional group isomers

Stereoisomerism:

• Geometrical isomers (cis/trans) in alkenes.

2. Key Patterns & Examples

General Formulas

• Alkanes: CₙH₂ₙ₊₂

• Alkenes: CₙH₂ₙ

• Alcohols: CₙH₂ₙ₊₂O

Common Functional Groups

• –OH → alcohols

• –COOH → acids

• C=C → alkenes

• –CHO → aldehydes

• C=O → ketones

Examples of Isomers

• C₄H₁₀ → butane & isobutane

• C₂H₆O → ethanol & dimethyl ether

3. Tips & Tricks for Exams

• Count carbons carefully when naming compounds.

• Identify the longest carbon chain.

• Locate functional groups and number the chain from the nearest end.

• For alkenes, the position of the double bond is crucial.

• Draw structural isomers systematically to avoid missing any.

• Remember: aromatic compounds do NOT undergo addition reactions.

4. Important Points to Remember

• Carbon’s ability to catenate (form chains) is key to organic chemistry.

• Isomers can have very different chemical and physical properties.

• Functional groups dictate reactivity.

• Homologous series show predictable trends.

Double bonds restrict rotation → leading to cis/trans isomerism.