5 Ways to Make Electrophilic Aromatic Substitution Approachable to Students

Introduction: Electrophilic Aromatic Substitution

Aromatic compounds are also called conjugated cycloalkenes. These are the organic compounds that have specific odors. These are unsaturated organic compounds that form planar rings. In these compounds, the two different types of covalent bonds can help to join the atoms to make the structure. Substitution reactions occur when an atom, functional group, or ion is substituted by another atom, functional group, or ion.

There are three main types of aromatic substitution reactions; electrophilic aromatic substitution reactions, radical nucleophilic aromatic substitution reactions, and nucleophilic aromatic substitution reactions. An electrophilic aromatic substitution reaction is a type of aromatic substitution reaction in which an atom attached to the aromatic ring is replaced by an electrophile. A radical nucleophilic aromatic substitution reaction is a chain process. In SRN1, the radicals and anions are the intermediates of the process. A nucleophilic aromatic substitution reaction is the kind of aromatic substitution reaction in which the nucleophile is placed in the position of leaving a group on an aromatic ring compound.

There are several facts that can be difficult for students to understand. At Labster, we compiled all the complexities students experience while learning about the electrophilic aromatic substitution. We provide five different methods to make electrophilic aromatic substitution simpler for students to understand. At the end of the topic, we will convince you why a Labster virtual simulation is an effective method for teachers to teach tough topics like an electrophilic aromatic substitution to their students. 

Figure: An image shows step 1 of the mechanism of electrophilic substitution from Labster's virtual laboratory of electrophilic aromatic substitution.

Why electrophilic aromatic substitution can be tricky to learn

There are three main reasons that can make electrophilic aromatic substitution a hard topic to remember.

1. It feels abstract

Aromatic organic chemistry contains several abstract concepts. Abstract concepts are those terms that cannot be seen by the human eye. Sometimes, learning about abstract concepts is a hard task for students. In electrophilic aromatic substitution, students need to remember many compounds, atoms, protons, and substitutions that they are not able to see with the naked eye. So, it is difficult for students to learn about electrophilic aromatic substitution.

2. Too many complex reactions

In electrophilic aromatic substitution, the main thing is the reaction and its mechanisms. There are several reactions that students need to remember. In these reactions, all the derivatives of benzenes are involved. Some students may find difficulties during learning about the reactions and the mechanisms. You cannot remember the reactions by only reading them from textbooks. It is important to understand the full mechanism of electrophilic aromatic substitution reactions.

3. It's content-heavy

When students learn about electrophilic aromatic substitution, it is important to have basic knowledge of organic chemistry, aromatic compounds, and types of aromatic compounds. These basic concepts are helpful to understand electrophilic aromatic substitution reactions. There are several examples of aromatic commands that can perform the electrophilic aromatic substitution. Students may not like this topic because it is difficult and time-consuming.  

5 ways to make electrophilic aromatic substitution a more approachable topic to understand

Since you are familiar with the reasons that make electrophilic aromatic substitution a complex topic to learn. There are five methods that help the students to remember the electrophilic aromatic substitution.

1. People behind the science

Henry Edward Armstrong

Henry Edward Armstrong was an English organic chemist who invented electrophilic aromatic substitution in aromatic compounds. He observed the substitution reaction in naphthalene. Naphthalene is mainly used in the synthetic dye industry. He also introduced a method for determining organic impurities in the water. In part of organic chemistry, he explained the occurrence of substitution reactions in hydrocarbon naphthalene. He proposed the mechanism of substitution of compounds which is closely related to the modern mechanism of electrophilic aromatic substitution. In 1887, Armstrong developed the ortho, meta, and para properties of ring reactions.

2. Basic knowledge of the electrophilic aromatic substitution mechanism

The electrophilic aromatic substitution reaction is a reaction in which an electrophile attacks the carbon atom to produce an intermediate cationic compound. Then, it leads to the elimination of a leaving group in the reaction. There are three main components present in an electrophilic aromatic substitution.

1. Formation of new sigma bonds.
2. When the bond between carbon and hydrogen breaks, it causes the removal of protons.
3. C=C bond is formed in the reaction that can help to maintain the aromaticity.

The mechanism of electrophilic aromatic substitution consists of two steps.

Step no. 1: At the beginning of the reaction, an electrophile is attacking the electrons present in the benzene ring. It can lead to the formation of positively changed cyclohexadienyl cations or arenium ions. The process of electrophile attack on the pi electrons is very slow and time-consuming. Furthermore, high activation of energy occurs due to the loss of aromaticity. The main factors are resonance, hindering, and probability which can be used for the determination of an electrophilic attack. This whole process is an endergonic reaction.

Step no. 2: In this step, a weak base is used for the deprotonation of the arenium ion. The carbonation intermediate which is formed in the first step can be attacked by a base. As a result, it can lose the proton. Then, another electron is used to create the pi bond and restore the aromaticity. This process is very fast and also exogenic. 

Figure: An image shows the two steps of the electrophilic aromatic substitution reaction from Labster's theory of electrophilic aromatic substitution. 

3. Types of electrophilic aromatic substitution

Students should learn about the main types of electrophilic aromatic substitution. It will help them to understand the topic. Additionally, they can differentiate between the reactions after learning the basic information about electrophilic aromatic substitution reactions. There are six main types of electrophilic aromatic substitution reactions.

1. Aromatic nitration reaction
2. Aromatic sulfonation reaction
3. Aromatic halogenation reaction
4. Friedel Crafts acylation reaction
5. Friedel Crafts alkylation reaction

Aromatic nitration reaction: In this reaction, the nitrogen atom attacks the hydrogen atom of the aromatic ring and replaces it. The main catalyst used in aromatic nitration reactions is sulfuric acid. The acid is helpful for the formation of nitronium ions.

Aromatic sulfonation reaction: The sulfonic acid is used to replace the hydrogen from the aromatic compound. Sulfuric acid and SO3 can be used to initiate protonation. These two molecules help to generate the protonation to perform the electrophilic aromatic substitution reaction.

Aromatic halogenation reaction: In an aromatic halogenation reaction, halogen such as bromide or chloride is used to replace the hydrogen atom from the substitution reaction. Lewis’s acid is helpful for the process of chlorination or bromination. In this process, a permanent bond is formed between the Cl-Cl or Br-Br molecules.

Friedel Crafts acylation reaction: When hydrogen is replaced by an acyl group, it is called Friedel Crafts acylation reaction. Two reagents are usually used in this reaction. The main catalyst used in Friedel Crafts acylation reaction is Lewis acid. There are acyl chlorides and carboxylic acid halides. The end product of this reaction is the formation of an aryl ketone.

Friedel Crafts alkylation reaction: In this reaction of the electrophilic aromatic substitution, the hydrogen atom is normally replaced with an alkyl group. The alkyl halide is used in combination with AlCl3 or FeCl3. Lewis acid is helpful to enhance the speed of Friedel Crafts alkylation reaction. There is a disadvantage of this reaction which is product amount can be increased as compared with the reactants. So, you may notice overalkylation in Friedel Crafts alkylation reaction.

4. Seeing is believing

Color diagrams are a great way to explain tough topics like electrophilic aromatic substitution. The diverse colors make the topic simpler and easier for students to understand. In electrophilic aromatic substitution, students need to learn about the structures, mechanisms, and chemical reactions. If students see color images of reactions, it will be easier for them to memorize the topic.

The image presented below shows the mechanism of electrophilic substitution. It helps to explain the cyclic structure of the aromatic compound and also the steps of the mechanism. The reaction has several steps in the electrophilic aromatic substitution. For instance, the intermediate step is carbocation intermediate and the final step is electrophilic aromatic substitution product. 

5. Use of virtual lab simulation

The virtual lab simulation is an advanced method that helps the students to learn difficult topics like electrophilic aromatic substitution. At Labster, we provide 3D simulations that have gamification elements like storytelling and the scoring system. These simulations are effective for teachers in conveying difficult topics to their students.

Labster virtual simulation on electrophilic aromatic substitution explains the mechanism of electrophilic aromatic substitution, classification of benzene substituents, resonance structures, and outcome of electrophilic aromatic substitution.

Check out Labster electrophilic aromatic substitution simulation here, or get in touch to find out how you can start using the virtual lab simulation for your students.