Question

250 ChemActivity 29 Electrophilic Aromatic Substitution no ChemActivity 29 Part A: Electrophilic Aromatic Substitution (What products are formed when a strong electrophile is added to benzene?) Model 1: (review) Electrophilic Addition of HCI Rani o g cyclohexene carbocation intermediate Run 2 U X benzene This product carbocation intermediate DOES NOT Critical Thinking Questions 1 For Rxn I (above) draw curved arrows showing the mechanism of electrophilic addition of HCl. Include an appropriate carbocation intermediate in the box above. Figure 1: Reaction Diagrams for Electrophilic Addition of HCI V.E. (Potential Energy) V.E. H-CI Reaction Progress (Rxn 1) Reaction Progress (Rxn 2) 2. Rxn 1 is slightly down-hill in terms of energy. Rxn 2 is very up-hill in terms of energy (see Figure 1). Construct an explanation for the large difference in energy between the reactants and the product in Ran 2. 3. Draw the carbocation that would form in Rxn 2. Explain why this carbocation goes back to the starting material (H-Cl and benzene) instead of forming the product.

Answer 1

1. Mechanism for the electrophilic addition along with carbocation intermediate is : + H-CI (Callocation Intermediate) 2. In the reaction 2, The initial reactant is aromatic while the intermediate and the product both are non aromatic and we know that stability of aromatic(low energy) compound is more than non aromatic (high energy) compounds. So there is large difference in energy of product and the reactants. 3. In this reaction 2, The initial reactant is aromatic while the intermediate and the product both are non aromatic and we know that stability of aromatic compound is more than non aromatic compounds so a large amount energy required for the product formation which makes the reaction endothermic. As the reaction always proceeds towards the more stable compound which in this case is reactant so this carbocation goes to reactants instead of products. + H-C1 e high blood Aromatic Mon- Aromatic 4. The reaction mechanism is explained below for the reaction: + Hal