Science Class 11 - Organic Chemistry Notes

Organic Chemistry

Welcome to the chapter on Organic Chemistry for Class 11. In this chapter, you will learn about the basics of organic chemistry, types of organic compounds, nomenclature, isomerism, and fundamental reactions. By the end of this chapter, you will be able to identify, name, and understand the properties and reactions of organic compounds.

Introduction

Organic chemistry is the branch of chemistry that deals with compounds containing carbon. Most of the compounds found in living things are organic. Organic chemistry is important in medicines, plastics, fuels, and many other materials we use every day.

Key Concepts

• Organic Compounds: Compounds mainly made of carbon and hydrogen, often with oxygen, nitrogen, sulfur, and halogens.
• Hydrocarbons: Compounds containing only carbon and hydrogen (alkanes, alkenes, alkynes).
• Functional Groups: Specific groups of atoms that give organic compounds their properties (e.g., alcohol, aldehyde, carboxylic acid).
• Nomenclature: The system of naming organic compounds according to IUPAC rules.
• Isomerism: Compounds with the same molecular formula but different structures or arrangements.

Classification of Organic Compounds

• Acyclic (Open Chain) Compounds: Compounds with straight or branched chains (e.g., alkanes, alkenes, alkynes).
• Cyclic (Closed Chain) Compounds: Compounds with ring structures (e.g., cyclohexane, benzene).
• Aromatic Compounds: Compounds containing benzene rings.
• Heterocyclic Compounds: Rings containing atoms other than carbon (e.g., pyridine).

Nomenclature of Organic Compounds

Organic compounds are named using IUPAC rules:

• Identify the longest carbon chain (parent chain).
• Number the chain so that the functional group gets the lowest possible number.
• Name and number the substituents (side groups).
• Combine the names in the correct order.

Example: CH₃CH₂OH is called ethanol.

Isomerism

• Structural Isomerism: Same molecular formula, different structures (e.g., butane and isobutane).
• Stereoisomerism: Same structure, different spatial arrangement (e.g., cis-trans isomers).

Fundamental Reactions in Organic Chemistry

• Substitution Reactions: One atom or group is replaced by another (common in alkanes and aromatic compounds).
• Addition Reactions: Atoms are added to double or triple bonds (common in alkenes and alkynes).
• Elimination Reactions: Atoms are removed from a molecule, forming double or triple bonds.
• Oxidation and Reduction: Addition or removal of oxygen/hydrogen atoms.

Practice Questions

1. What is the difference between alkanes and alkenes?
2. Name the functional group in CH₃COOH.
3. Write the IUPAC name for CH₃CH₂CH₃.
4. What is structural isomerism? Give an example.
5. What type of reaction is the conversion of ethene to ethane?

Challenge Yourself

• Draw the structures of butane and isobutane. Show how they are isomers.
• Write the IUPAC names for the first five alkanes.

Did You Know?

• There are millions of organic compounds, far more than inorganic compounds!
• Plastic, medicines, and even DNA are made of organic molecules.

Glossary

• Hydrocarbon: Compound made of only carbon and hydrogen.
• Functional Group: A group of atoms responsible for the characteristic reactions of a compound.
• Isomer: Compounds with the same molecular formula but different structures.
• IUPAC: International Union of Pure and Applied Chemistry, which sets rules for naming compounds.

Answers to Practice Questions

1. Alkanes have only single bonds; alkenes have at least one double bond.
2. Carboxylic acid group (-COOH).
3. Propane.
4. Structural isomerism is when compounds have the same molecular formula but different structures. Example: butane and isobutane.
5. Addition reaction.

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Organic chemistry is everywhere! Keep practicing to master the basics and discover the world of carbon compounds.