Diagrams drawn for the propagation steps of radical bromination of benzene should be identified as either representative of early or late transition states. Concept introduction: Hammond postulate states that exothermic reactions are characterized by early transition states that resemble the structure of substrate more than the product. Slow or endothermic processes are characterized by late transition states that resemble the almost formed bonds as in the products. Analogous to hydrocarbons the benzene can also undergo initiation to generate bromine radicals; propagation of radicals formed and finally termination. This sequence can be outlined as follows: Step1: Initiation via homolytic cleavage of Br − Br bond: Br 2 initiates the reaction; undergoes homolysis and forms bromine radical atom. Energy for homolytic cleavage is provided by the heat or ultraviolet light. Step2: Propagation: In first of the propagation steps bromine radical from step 1 abstracts hydrogen radical from C 6 H 6 as follows: In subsequent propagation step,phenyl radical abstracts Br · radical from another Br 2 , and liberates bromobenzene and new bromine radical. Step3: Termination: Bromine radicals generated in propagation steps get quenched upon combination with one another illustrated as follows:

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Formula Formula Bond dissociation energy (BDE) is the energy required to break a bond, making it an endothermic process. BDE is calculated for a particular bond and therefore consists of fragments such as radicals since it undergoes homolytic bond cleavage. For the homolysis of a X-Y molecule, the energy of bond dissociation is calculated as the difference in the total enthalpy of formation for the reactants and products. X-Y → X + Y BDE = Δ H f X + Δ H f Y – Δ H f X-Y where, ΔHf is the heat of formation.

Chapter 3, Problem 26P

Interpretation Introduction

Interpretation:Diagrams drawn for the propagation steps of radical bromination of benzene should be identified as either representative of early or late transition states.

Concept introduction:Hammond postulate states that exothermic reactions are characterized by early transition states that resemble the structure of substrate more than the product. Slow or endothermic processes are characterized by late transition states that resemble the almost formed bonds as in the products.

Analogous to hydrocarbons the benzene can also undergo initiation to generate bromine radicals; propagation of radicals formed and finally termination. This sequence can be outlined as follows:

Step1: Initiation via homolytic cleavage of Br−Br bond: Br2 initiates the reaction; undergoes homolysis and forms bromine radical atom. Energy for homolytic cleavage is provided by the heat or ultraviolet light.

Step2: Propagation: In first of the propagation steps bromine radical from step 1 abstracts hydrogen radical from C6H6 as follows:

In subsequent propagation step,phenyl radical abstracts Br· radical from another Br2 , and liberates bromobenzene and new bromine radical.

Step3: Termination: Bromine radicals generated in propagation steps get quenched upon combination with one another illustrated as follows:

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Answer 2

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Formula Formula Bond dissociation energy (BDE) is the energy required to break a bond, making it an endothermic process. BDE is calculated for a particular bond and therefore consists of fragments such as radicals since it undergoes homolytic bond cleavage. For the homolysis of a X-Y molecule, the energy of bond dissociation is calculated as the difference in the total enthalpy of formation for the reactants and products. X-Y → X + Y BDE = Δ H f X + Δ H f Y – Δ H f X-Y where, ΔHf is the heat of formation.

Chapter 3, Problem 26P

Interpretation Introduction

Interpretation:Diagrams drawn for the propagation steps of radical bromination of benzene should be identified as either representative of early or late transition states.

Concept introduction:Hammond postulate states that exothermic reactions are characterized by early transition states that resemble the structure of substrate more than the product. Slow or endothermic processes are characterized by late transition states that resemble the almost formed bonds as in the products.

Analogous to hydrocarbons the benzene can also undergo initiation to generate bromine radicals; propagation of radicals formed and finally termination. This sequence can be outlined as follows:

Step1: Initiation via homolytic cleavage of Br−Br bond: Br2 initiates the reaction; undergoes homolysis and forms bromine radical atom. Energy for homolytic cleavage is provided by the heat or ultraviolet light.

Step2: Propagation: In first of the propagation steps bromine radical from step 1 abstracts hydrogen radical from C6H6 as follows:

In subsequent propagation step,phenyl radical abstracts Br· radical from another Br2 , and liberates bromobenzene and new bromine radical.

Step3: Termination: Bromine radicals generated in propagation steps get quenched upon combination with one another illustrated as follows:

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Answer 3

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Formula Formula Bond dissociation energy (BDE) is the energy required to break a bond, making it an endothermic process. BDE is calculated for a particular bond and therefore consists of fragments such as radicals since it undergoes homolytic bond cleavage. For the homolysis of a X-Y molecule, the energy of bond dissociation is calculated as the difference in the total enthalpy of formation for the reactants and products. X-Y → X + Y BDE = Δ H f X + Δ H f Y – Δ H f X-Y where, ΔHf is the heat of formation.

Chapter 3, Problem 26P

Interpretation Introduction

Interpretation:Diagrams drawn for the propagation steps of radical bromination of benzene should be identified as either representative of early or late transition states.

Concept introduction:Hammond postulate states that exothermic reactions are characterized by early transition states that resemble the structure of substrate more than the product. Slow or endothermic processes are characterized by late transition states that resemble the almost formed bonds as in the products.

Analogous to hydrocarbons the benzene can also undergo initiation to generate bromine radicals; propagation of radicals formed and finally termination. This sequence can be outlined as follows:

Step1: Initiation via homolytic cleavage of Br−Br bond: Br2 initiates the reaction; undergoes homolysis and forms bromine radical atom. Energy for homolytic cleavage is provided by the heat or ultraviolet light.

Step2: Propagation: In first of the propagation steps bromine radical from step 1 abstracts hydrogen radical from C6H6 as follows:

In subsequent propagation step,phenyl radical abstracts Br· radical from another Br2 , and liberates bromobenzene and new bromine radical.

Step3: Termination: Bromine radicals generated in propagation steps get quenched upon combination with one another illustrated as follows:

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Answer 4

Question

Formula Formula Bond dissociation energy (BDE) is the energy required to break a bond, making it an endothermic process. BDE is calculated for a particular bond and therefore consists of fragments such as radicals since it undergoes homolytic bond cleavage. For the homolysis of a X-Y molecule, the energy of bond dissociation is calculated as the difference in the total enthalpy of formation for the reactants and products. X-Y → X + Y BDE = Δ H f X + Δ H f Y – Δ H f X-Y where, ΔHf is the heat of formation.

Chapter 3, Problem 26P

Interpretation Introduction