The Kharasch reaction, named after its discoverer who also invented the medical preservative thimerosal, is a radical process in which carbon tetrachloride is added across ar alkene. Draw a mechanism showing initiation and propagation steps for this reaction and explaining the observed regiochemical outcome. ÇI .Cl3 Cl4, heat R R Ph. Ph

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### The Kharasch Reaction

The Kharasch reaction, named after its discoverer who also invented the medical preservative thimerosal, is a radical process in which carbon tetrachloride is added across an alkene. Draw a mechanism showing initiation and propagation steps for this reaction and explaining the observed regiochemical outcome.

#### Reaction Description:
- **Reactants and Reagents:** An alkene (R group attached) reacts with carbon tetrachloride (CCl4) in the presence of heat.
- **Product:** The product is a compound where the alkene has been transformed, and chlorine (Cl) along with a trichloromethyl group (CCl3) have been added across the double bond.

#### Mechanism:
To fully understand the reaction, it's critical to elucidate the initiation and propagation stages of the radical process. The radical mechanism typically involves three phases: initiation, propagation, and termination.

1. **Initiation:**
   - Heat induces homolytic cleavage of the peroxide, producing two alkoxy radicals.
   - Alkoxy radicals abstract chlorine atoms from CCl4, generating trichloromethyl radicals (CCl3•).

2. **Propagation:**
   - The trichloromethyl radical adds to the double bond of the alkene, generating a new carbon-centered radical.
   - The carbon-centered radical abstracts a chlorine atom from another molecule of CCl4, yielding the final product and regenerating the trichloromethyl radical.

3. **Termination:**
   - Involves radical recombination leading to non-radical products, but this part is often less emphasized if propagation steps are efficient in maintaining the radical chain.

#### Observed Regiochemical Outcome:
- The addition of Cl and CCl3 across the double bond can be explained by the stability of the intermediary radicals formed during the propagation steps. The reaction proceeds regioselectively, forming the most stable radical intermediate.

**Illustration:**

\[ \text{ \begin{array}{c} \ce{R-CH=CH2} \\ \ce{|} \\ \text{Alkene} \end{array} \xrightarrow{\text{CCl4, heat}} \ce{\qquad\longrightarrow \begin{array}{c} \ce{R-CH(Cl)-CH2-CCl3} \\ \text{Product} \end{array}} \]

This detailed breakdown of the K
Transcribed Image Text:### The Kharasch Reaction The Kharasch reaction, named after its discoverer who also invented the medical preservative thimerosal, is a radical process in which carbon tetrachloride is added across an alkene. Draw a mechanism showing initiation and propagation steps for this reaction and explaining the observed regiochemical outcome. #### Reaction Description: - **Reactants and Reagents:** An alkene (R group attached) reacts with carbon tetrachloride (CCl4) in the presence of heat. - **Product:** The product is a compound where the alkene has been transformed, and chlorine (Cl) along with a trichloromethyl group (CCl3) have been added across the double bond. #### Mechanism: To fully understand the reaction, it's critical to elucidate the initiation and propagation stages of the radical process. The radical mechanism typically involves three phases: initiation, propagation, and termination. 1. **Initiation:** - Heat induces homolytic cleavage of the peroxide, producing two alkoxy radicals. - Alkoxy radicals abstract chlorine atoms from CCl4, generating trichloromethyl radicals (CCl3•). 2. **Propagation:** - The trichloromethyl radical adds to the double bond of the alkene, generating a new carbon-centered radical. - The carbon-centered radical abstracts a chlorine atom from another molecule of CCl4, yielding the final product and regenerating the trichloromethyl radical. 3. **Termination:** - Involves radical recombination leading to non-radical products, but this part is often less emphasized if propagation steps are efficient in maintaining the radical chain. #### Observed Regiochemical Outcome: - The addition of Cl and CCl3 across the double bond can be explained by the stability of the intermediary radicals formed during the propagation steps. The reaction proceeds regioselectively, forming the most stable radical intermediate. **Illustration:** \[ \text{ \begin{array}{c} \ce{R-CH=CH2} \\ \ce{|} \\ \text{Alkene} \end{array} \xrightarrow{\text{CCl4, heat}} \ce{\qquad\longrightarrow \begin{array}{c} \ce{R-CH(Cl)-CH2-CCl3} \\ \text{Product} \end{array}} \] This detailed breakdown of the K
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