11. Radical Reactions

In the following molecules, identify the carbon where the radical is most likely to form in the first propagation step.

(c)

The halogenation of an alkane when there is an alkene present in the molecule does not proceed with the regioselectivity you might expect. Using principles similar to those developed in this chapter, rationalize the formation of A as the only product. We study this reaction further in Chapter 8.

Predict the major product(s) of the following allylic bromination reactions.

(d)

The fact that allylic halogenation results in formation of the most stable alkene suggests that it is under thermodynamic control. Thus, the second propagation step must be reversible. Suggest an arrow-pushing mechanism by which the less stable allylic halide might equilibrate to the more stable allylic halide.

Predict the major product(s) of the following allylic bromination reactions.

(c)

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

(c)

Propose a mechanism to account for the products formed in the following reaction:

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

(b)

How many allylic substituted bromoalkenes are formed from the reactions in Problems 18 if stereoisomers are included?

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

a.

Give a mechanism to explain the two products formed in the following reaction.

When methylenecyclohexane is treated with a low concentration of bromine under irradiation by a sunlamp, two substitution products are formed.

a. Propose structures for these two products. (b) Propose a mechanism to account for their formation.

Predict the products of the following reactions.

(c) 2-methylpropene + NBS, light

Predict the products of the following allylic halogenation reactions.

(c)

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

(c)