Lesson Plan | Traditional Methodology | Organic Reactions: Substitution

Objectives

Duration: (10 - 15 minutes)

This stage is fundamental to introduce students to the topic of substitution reactions in organic chemistry. The goal is to provide an overview of the skills that will be developed throughout the class, preparing students for a detailed understanding of the types of reactions, catalysts involved, synthetic routes, and the products generated. This establishes a solid foundation for subsequent learning and ensures that students know which knowledge and skills they should acquire.

Main Objectives

1. Understand the main substitution reactions in organic compounds.

2. Identify the catalysts used in substitution reactions.

3. Recognize synthetic routes and the products resulting from substitution reactions.

Introduction

Duration: (10 - 15 minutes)

The purpose of this stage is to spark students' interest and prepare them for the content to be covered. By presenting the context and curiosities, students can see the practical applicability of substitution reactions, which may increase their motivation and engagement with the topic. Moreover, this introduction serves to connect students' prior knowledge with the new concepts that will be presented, facilitating understanding and retention of information.

Context

To start the class on substitution reactions in organic compounds, it is important to contextualize students about the relevance of these reactions. Explain that substitution reactions are fundamental in organic chemistry as they allow for the modification of molecules to create new compounds with desired properties. They are widely used in the synthesis of medications, the production of polymers, and industrial processes. Mention that by understanding these reactions, students will be able to better comprehend how organic compounds are manipulated and applied in various areas of science and technology.

Curiosities

Did you know that aspirin, one of the most common medications in the world, is produced through a substitution reaction? The synthesis of aspirin involves the substitution of a hydroxyl group for an acetyl group in salicylic acid. This is just one example of how substitution reactions are crucial in pharmacology and in the production of medications that we use daily.

Development

Duration: (60 - 70 minutes)

The purpose of this stage is to provide students with a detailed understanding of substitution reactions, their mechanisms, the catalysts involved, and their practical applications. By addressing these topics in a structured and detailed manner, the teacher ensures that students acquire deep knowledge and can apply these concepts in different contexts, such as in drug synthesis and industrial production.

Covered Topics

1. Nucleophilic Substitution Reaction (SN1 and SN2): Explain what nucleophilic substitution reactions are. Detail the differences between the SN1 and SN2 mechanisms, including the factors that influence each type of reaction, such as substrate structure, nucleophile nature, solvent, and reaction kinetics. 2. Electrophilic Substitution Reaction (SE): Describe electrophilic substitution reactions, highlighting aromatic compounds as the main substrates. Explain the reaction mechanism, including the formation of the activated complex and the importance of directing groups. Provide common examples, such as the nitration and halogenation of benzene. 3. Catalysts in Substitution Reactions: Address the importance of catalysts in substitution reactions. Explain how catalysts increase the reaction rates and provide examples of common catalysts, such as Lewis acids and bases. Detail the role of catalysts in specific reactions, such as the halogenation of alkanes and esterification. 4. Synthetic Routes and Products of Substitution Reactions: Explain how substitution reactions are used in synthetic routes to obtain different organic compounds. Present examples of synthetic routes that involve several substitution steps to produce medications, polymers, and other chemicals of industrial interest.

Classroom Questions

1. Describe the main differences between the mechanisms of SN1 and SN2 reactions, including the factors that influence each type of reaction. 2. Explain the role of catalysts in substitution reactions and provide examples of common catalysts used in different reactions. 3. Discuss how substitution reactions can be applied in synthetic routes to produce organic compounds of industrial interest, providing specific examples.

Questions Discussion

Duration: (15 - 20 minutes)

The purpose of this stage is to review and consolidate students' learning, ensuring that they deeply understand the concepts covered. The detailed discussion of the questions allows students to verify their answers and correct possible misconceptions. Furthermore, the proposed questions and reflections encourage active engagement from students, promoting a collaborative and critical learning environment where students can explore and apply concepts practically.

Discussion

• Explain the main differences between the mechanisms of SN1 and SN2 reactions, including the factors that influence each type of reaction. Response: SN1 (Unimolecular Nucleophilic Substitution) and SN2 (Bimolecular Nucleophilic Substitution) differ mainly in their mechanisms and factors influencing each reaction type. SN1 occurs in two steps: formation of an intermediate carbocation and subsequent nucleophilic attack. SN2 occurs in a single step, where the nucleophile simultaneously attacks as the leaving group exits the molecule. Factors such as substrate structure (SN1 favors tertiary substrates, while SN2 favors primary substrates), the strength of the nucleophile (SN2 requires strong nucleophiles), and the solvent (SN1 favors protic polar solvents, while SN2 favors aprotic polar solvents) are determinants.

• Explain the role of catalysts in substitution reactions and provide examples of common catalysts used in different reactions. Response: Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. In substitution reactions, catalysts such as Lewis acids (e.g., AlCl3) and bases (e.g., NaOH) are common. They function by increasing the reactivity of the reactants or stabilizing reactive intermediates. For example, in halogenation reactions of alkanes, chlorine or bromine is often activated by ultraviolet light or heat, while in esterification, a strong acid like sulfuric acid is used to speed up the reaction.

• Discuss how substitution reactions can be applied in synthetic routes to produce organic compounds of industrial interest, providing specific examples. Response: Substitution reactions are fundamental in synthetic routes for producing various organic compounds. In drug synthesis, for example, the chlorination of benzene followed by nucleophilic substitution can lead to the formation of analgesics like paracetamol. In polymer production, substitution reactions are used to modify monomers, such as in the preparation of polyesters by substituting hydroxyl groups for ester groups. Another example is the manufacture of industrial chemicals, like the synthesis of pesticides and dyes, which often involve multiple substitution steps to introduce desired functional groups.

Student Engagement

1. How does the structure of the substrate influence the choice between an SN1 and SN2 reaction? 2. What are the factors that determine the strength of a nucleophile in substitution reactions? 3. Why do protic polar solvents favor SN1 reactions while aprotic polar solvents favor SN2? 4. Give examples of substitution reactions where a Lewis acid acts as a catalyst. Explain the mechanism of action. 5. How would you apply the concept of substitution reactions in the synthesis of a new drug? Describe a hypothetical synthetic route. 6. What is the importance of directing groups in electrophilic substitution reactions in aromatic compounds?

Conclusion

Duration: (5 - 10 minutes)

The purpose of this stage is to review and consolidate learning, ensuring that students understand the main concepts discussed during the class. The conclusion helps reinforce the connection between theory and practice, highlighting the importance of substitution reactions in the scientific and industrial context, and encouraging students to apply this knowledge in real-life situations.

Summary

• Introduction to substitution reactions in organic compounds.
• Difference between nucleophilic substitution reactions SN1 and SN2.
• Mechanism of electrophilic substitution reactions in aromatic compounds.
• Importance of catalysts in substitution reactions.
• Applications of substitution reactions in synthetic routes for the production of medications, polymers, and other chemicals.

The class connected the theory of substitution reactions with their practical applications, showing how these mechanisms are essential in the synthesis of organic compounds used in medications, polymers, and industrial processes. Real examples, such as the production of aspirin and the halogenation of benzene, helped illustrate the relevance of these reactions in daily life and the chemical industry.

Substitution reactions are fundamental for creating new compounds with desired properties, directly impacting areas such as pharmacology, material production, and the chemical industry. Understanding these processes allows students to recognize the importance of these reactions in producing medications, like aspirin, and in manufacturing essential materials for modern society, such as polymers and pesticides.