11. Radical Reactions

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)

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.

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.

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

b. The bromination of cyclohexene using NBS gives only one major product, as shown on the previous page. Explain why there is no second product from an allylic shift.

Using 1,2-dimethylcyclohexene as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.) If a chiral product is shown, assume that it is part of a racemic mixture.

(a)

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

(a)

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

(c)

Suggest a mechanism for the following reactions.

(c)

Identify the two different alkenes that undergo allylic halogenation to prepare the compound shown.

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

(c)

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

(d)

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)

Predict the products of the following allylic halogenation reactions.

(a)