Chemistry Lesson Note On Isomerism – Structural and Geometric On

Topic: Isomerism – Structural and Geometric

Class: SS1

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Specific Objectives:

By the end of the lesson, students should be able to:

1. Define isomerism.
2. Differentiate between structural and geometric isomerism.
3. Identify and draw examples of structural and geometric isomers.
4. Explain the significance of isomerism in organic chemistry.

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Instructional Materials:

• Molecular model kits
• Charts showing structural and geometric isomers
• Whiteboard and markers
• Organic compound samples or printed diagrams

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Lesson Content:

Step 1: Definition of Isomerism

Isomerism is the phenomenon whereby two or more compounds have the same molecular formula but different structural or spatial arrangements of atoms, resulting in different properties.

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Step 2: Types of Isomerism

There are two main types at this level:

1. Structural Isomerism – Also known as constitutional isomerism, it arises from different arrangements of atoms within the molecule.

2. Geometric Isomerism (Cis-Trans Isomerism) – A form of stereoisomerism where compounds have the same molecular and structural formulas but differ in the spatial arrangement around a double bond.

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Step 3: Structural Isomerism

Types of structural isomerism:

• Chain isomerism: Different arrangements of the carbon chain (e.g., butane vs. methylpropane).
• Position isomerism: Same functional group but different position on the carbon chain (e.g., but-1-ene vs. but-2-ene).
• Functional group isomerism: Same molecular formula but different functional groups (e.g., ethanol vs. dimethyl ether).

Example:

C₄H₁₀ can be:

• Butane: CH₃–CH₂–CH₂–CH₃
• 2-Methylpropane: (CH₃)₃CH

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Step 4: Geometric Isomerism

Occurs in compounds with a double bond and two different groups on each carbon of the bond.

• Cis-isomer: Similar groups on the same side of the double bond.
• Trans-isomer: Similar groups on opposite sides of the double bond.

Example:

But-2-ene:

• Cis-but-2-ene: CH₃–CH=CH–CH₃ (CH₃ groups on the same side)
• Trans-but-2-ene: CH₃–CH=CH–CH₃ (CH₃ groups on opposite sides)

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Evaluation:

1. Define isomerism.
2. Differentiate between structural and geometric isomerism.
3. Give one example each of chain, position, and functional group isomerism.
4. Draw the cis and trans forms of but-2-ene.
5. Explain why geometric isomerism does not occur in alkanes.

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Homework:

1. List three types of structural isomerism and give one example of each.
2. Draw and name two structural isomers of pentane.
3. Explain the condition necessary for geometric isomerism to occur.

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Conclusion:

Isomerism shows that compounds with the same molecular formula can exhibit different physical and chemical properties due to differences in structure or spatial arrangement. This concept is fundamental in understanding the diversity of organic compounds.

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