11. Radical Reactions

In the presence of a small amount of bromine, cyclohexene undergoes the following light-promoted reaction:

d. Explain why cyclohexene reacts with bromine much faster than cyclohexane, which must be heated to react.

Show the products you expect when each compound reacts with NBS with light shining on the reaction.

(a)

(b)

In the presence of a small amount of bromine, the following light-promoted reaction has been observed.

a. Write a mechanism for this reaction. Your mechanism should explain how both products are formed. (Hint: Notice which H atom has been lost in both products.)

Provide the mechanism of the radical reactions shown.

(b)

Two products are formed when methylenecyclohexane reacts with NBS? Show how each is formed. Disregard stereoisomers.

In the presence of a small amount of bromine, the following light-promoted reaction has been observed.

b. Explain why only this one type of hydrogen atom has been replaced, in preference to any of the other hydrogen atoms in the starting material.

In the following allylic radicals, identify the carbon where the new C― Br bond is most likely to form in the second propagation step.

(b)

What is the major product of the following reactions? Disregard stereoisomers:

b.

How many allylic substituted bromoalkenes are formed from the reactions in Problems 17 if stereoisomers are included?

Draw the products of the following reactions, including all stereoisomers:

c.

In the presence of a small amount of bromine, cyclohexene undergoes the following light-promoted reaction:

a. Propose a mechanism for this reaction.

What is the major product of the following reactions? Disregard stereoisomers:

d.

The light-initiated reaction of 2,3-dimethylbut-2-ene with N-bromosuccinimide (NBS) gives two products:

a. Give a mechanism for this reaction, showing how the two products arise as a ­consequence of the resonance-stabilized intermediate.

Propose mechanisms to account for the observed products in the following reactions.

(a)