11. Radical Reactions

Explain why the rate of bromination of methane decreases if HBr is added to the reaction mixture.

How many alkyl halides are obtained from monochlorination of the alkanes in Problem 4 if stereoisomers are included?

c.

How many monochlorination products would be obtained if all stereoisomers are included?

What is the major product obtained from treating an excess of each of the following compounds with Cl₂ in the presence of ultraviolet light at room temperature? Disregard stereoisomers.

a.

In the presence of an acid catalyst, acetaldehyde forms a trimer known as paraldehyde. Because it induces sleep when it is administered to animals in large doses, paraldehyde is used as a sedative or hypnotic. Propose a mechanism for the formation of paraldehyde.

Propose a mechanism for the following reaction:

How many alkyl halides are obtained from monochlorination of the alkanes in Problem 4 if stereoisomers are included?

d.

How many monochlorination products can be obtained from the radical chlorination of methylcyclohexane? Disregard stereoisomers.

Write the steps for formation of tetrachloromethane (CCl₄) from the reaction of methane with Cl₂ + hv.

A possible alternative mechanism to that shown in Problem 47 for the monochlorination of methane involves the following propagation steps:

How do you know that the reaction does not take place by this mechanism?

If cyclopentane reacts with more than one equivalent of Cl₂ at a high temperature, how many dichlorocyclopentanes would you expect to obtain as products?

Show how you would prepare cyclopentene from each compound.

c. cyclopentane (not by dehydrogenation)

Each of the following proposed mechanisms for the free-radical chlorination of methane is wrong. Explain how the experimental evidence disproves each mechanism.

a.

a. Propose a mechanism for the free-radical chlorination of ethane,

a. Draw the structure of the transition state for the second propagation step in the chlorination of methane.

Show whether the transition state is product-like or reactant-like and which of the two partial bonds is stronger.