Lesson plan of Introduction to Organic Chemistry: Aromatic Compounds

Objectives (5 - 10 minutes)

1. Comprehend the definition of aromatic compounds: Students should be able to define aromatic compounds clearly and concisely, highlighting their key features, such as the presence of benzene rings and the presence of conjugated pi bonds. They should understand that aromatic compounds are a special class of organic compounds that have unique properties due to the presence of benzene rings.

2. Recognize structures of aromatic compounds: Students should be able to identify and represent structures of aromatic compounds. They should learn to correctly draw benzene rings and identify conjugated pi bonds. This skill is fundamental for understanding how aromatic compounds react and interact.

3. Differentiate between aromatic and non-aromatic compounds: Students should be able to distinguish between aromatic and non-aromatic compounds, identifying the characteristics that make a compound aromatic. They should understand that not all organic compounds that contain benzene rings are aromatic and that aromaticity is a special property.

Secondary objectives:

• Apply gained knowledge to practical situations: Students should be able to apply what they have learned about aromatic compounds to practical situations. For example, they may be asked to identify whether a compound is aromatic or non-aromatic based on its structure.
• Develop critical thinking skills: By learning about aromatic compounds, students should develop critical thinking skills, such as the ability to analyze and evaluate information, make connections between concepts, and solve complex problems.

Introduction (10 - 15 minutes)

1. Review of previous content: The teacher will start the class by reviewing important concepts that will be needed for understanding the current topic. This will include a quick review on organic compounds, covalent bonds, and pi bonds. The review can be done by asking students direct questions to activate their prior knowledge.

2. Problem situation: The teacher will present two situations that will spark the interest of the students and motivate them to learn about aromatic compounds:

   • Situation 1: The teacher can mention that benzene, an aromatic compound, is one of the most widely used chemicals in the industry. Students can be asked about the importance of understanding the properties of benzene given its wide use.

   • Situation 2: The teacher can present a clinical case of a rare disease called Porphyria which is related to the inability of the body to properly metabolize some aromatic compounds. Students can be challenged to think about how a lack of understanding of these compounds can lead to medical conditions.

3. Contextualization: The teacher will explain the importance of aromatic compounds in the real world. It can be mentioned that these compounds are widely used in the pharmaceutical industry, in the production of plastics, dyes, perfumes, and many other products. Also, the understanding of these compounds is crucial for research in several areas, including medicine, environmental chemistry, and biology.

4. Introduction to the topic: In order to gain the attention of the students, the teacher can introduce the topic in an interesting and engaging way. Here are some suggestions:

   • Curiosity 1: The teacher can mention that benzene, one of the most known aromatic compounds, was discovered by Michael Faraday in 1825 while trying to isolate a colourless liquid from a sample of whale oil. Faraday named it "benzene" after the German word "benzol", which refers to a similar liquid obtained from turpentine resin.

   • Curiosity 2: The teacher can mention that the structure of benzene - a six-carbon ring with alternating double bonds - was proposed by August Kekulé in 1865 in a dream he had of a snake biting its own tail, forming a ring.

   • Practical application: The teacher can mention that the understanding of aromatic compounds is crucial for the pharmaceutical industry. For example, many medicines, like aspirin and penicillin, are aromatic compounds. A lack of understanding of these compounds can lead to mistakes in the production of drugs or in the comprehension of how they work in the body.

Development (20 - 25 minutes)

1. Theory: Definition and Characteristics of Aromatic Compounds (5 - 7 minutes)

   • Definition: The teacher should explain that aromatic compounds are a special group of organic compounds that have benzene rings in their structure. These rings are characterized for having alternating double bonds and a delocalized pi electron cloud above and below the plane of the ring. The teacher can illustrate this structure on the board.

   • Characteristics: The teacher should highlight the following characteristics of aromatic compounds:

     1. Stability: Due to their delocalized pi electron cloud, aromatic compounds are more stable than aliphatic compounds, which are characterized to have sigma bonds between their carbon atoms.
     2. Reactivity: Aromatic compounds are less reactive than aliphatic compounds, since the delocalization of electrons in the pi cloud makes it harder to break the pi bonds.
     3. Electric Conductivity: Aromatic compounds don't conduct electricity since they don't have free electrons to carry the electrical current.

2. Theory: Structure and Representation of Aromatic Compounds (5 - 7 minutes)

   • Structure: The teacher should explain that benzene rings can be represented in several ways, but the most common representation is the hexagon with a circle inside. He/she should emphasize that, although the circle might seem like just a way of simplifying the representation, it actually represents the delocalized pi electron cloud.

   • Representation: The teacher should teach the students how to draw the structure of an aromatic compound from its molecular formula. He/she should explain that each carbon in the benzene ring must be bonded to a hydrogen, and that the molecular formula of an aromatic compound will always be a multiple of 6, plus 6 (because of the hydrogens). The teacher can give examples of molecular formulas and ask the students to draw the corresponding structure.

3. Theory: Aromaticity and Non-Aromaticity (5 - 7 minutes)

   • Aromaticity: The teacher should explain that not all organic compounds that contain benzene rings are aromatic. To be aromatic, a compound must fit three criteria:

     1. The ring must be planar: The carbon atoms in the benzene ring must all lie in the same plane.
     2. The ring must be conjugated: All the atoms in the ring must be sp² hybridized, which means they must have a pi bond in their plane.
     3. The ring must have 4n+2 pi electrons (where n is any non-negative integer): This is Hückel's rule, which determines whether a ring is aromatic. If the ring has 4n+2 pi electrons, it is aromatic; if it has 4n pi electrons, it is antiaromatic; if it has any other number of pi electrons, it is non-aromatic. The teacher can give examples of rings with different numbers of pi electrons and ask the students to determine if they are aromatic, antiaromatic, or non-aromatic.

   • Non-Aromaticity: The teacher should explain that non-aromatic (or aliphatic) compounds don't fit one or more of the criteria of aromaticity. This means they are less stable and more reactive than aromatic compounds. The teacher can give examples of non-aromatic compounds and ask the students to identify why they are not aromatic.

4. Practical Activity: After the theoretical explanation, students will be asked to draw the structures of several aromatic and non-aromatic compounds in their notebooks, based on their molecular formulas. The teacher will be circulating around the room to help the students and clarify any doubts they might have.

Feedback (10 - 15 minutes)

1. Group Discussion (5 - 7 minutes)

   • The teacher should promote a group discussion where students can share the structures they have drawn and the conclusions they have reached about the aromaticity of the compounds. In this moment, the teacher should reinforce the concepts that have been discussed, correct any possible mistake, and clarify any doubts that might have arisen during the practical activity.
   • The teacher can ask direct questions to stimulate the discussion, like: "Why do you think this compound is aromatic?" or "How can you determine if a compound is aromatic or not just by looking at its structure?"
   • Also, the teacher can ask the students to share their insights about the importance of aromatic compounds in the real world, based on the practical applications that were discussed during the Introduction.

2. Connection to Theory (3 - 5 minutes)

   • The teacher should ask the students to reflect on the practical activity and make connections to the theory that has been presented. They can be questioned about how the structure of a compound determines whether it is aromatic or not, and how aromaticity affects the properties and reactivity of the compounds.
   • The teacher can also ask the students to share the strategies that they used to determine whether a compound was aromatic or not, and how they applied the criteria of aromaticity. This can help to identify any concepts that the students might have not completely understood and that need further reinforcement.

3. Individual Reflection (2 - 3 minutes)

   • To finish the class, the teacher should ask the students to make an individual reflection about what they have learned. They can be asked to think about the following questions:
     1. What was the most important concept you have learned today?
     2. What questions do you still have about aromatic compounds?
   • The teacher can ask the students to write their answers in their notebooks and to share them in the next class. This will allow the teacher to adjust his/her future classes to address any gaps in the understanding of the students and to answer any questions they might have.

4. Feedback from the Teacher (1 minute)

   • Finally, the teacher should give feedback to the students about the class, highlighting the strengths and identifying areas that need improvement. The teacher can compliment the active participation of the students in the discussion and in the practical activity, and encourage them to keep asking questions and seeking answers to their doubts.

Conclusion (5 - 10 minutes)

1. Summary of the Content (2 - 3 minutes)

   • The teacher should recapitulate the main points that have been discussed during the class, reinforcing the definition of aromatic compounds, their characteristics, like the presence of benzene rings and conjugated pi bonds, and the criteria of aromaticity. The teacher can do a quick review asking the students to share what they remember about each point.

2. Connection between Theory and Practice (1 - 2 minutes)

   • The teacher should highlight how the class has connected theory with practice. This can be done by reminding the students about the practical activity of drawing the structures of aromatic and non-aromatic compounds, and how this activity helped to reinforce the theoretical concepts that were discussed.

3. Complementary Materials (1 - 2 minutes)

   • The teacher should suggest to the students additional study materials to deepen their understanding of the topic. This could include chemistry textbooks, chemistry educational websites, explanatory videos online and practical activities that the students can do at home to reinforce what they have learned in class.
   • The teacher can also suggest the students to do more research about the applications of aromatic compounds in industry and medicine, and to reflect about the importance of these compounds in their daily lives.

4. Relevance of the Subject (1 minute)

   • Finally, the teacher should emphasize the importance of studying aromatic compounds for everyday life. It can be mentioned that aromatic compounds have applications in many aspects of modern life, from the production of medicines to the manufacturing of plastics and perfumes. Also, the understanding of aromatic compounds is fundamental for research in several areas, including medicine, environmental chemistry, and biology.
   • The teacher can encourage the students to think about how what they have learned in class applies to the world around them, and how understanding aromatic compounds can help them to better understand the products they use and the scientific issues that they face today.