11. Radical Reactions

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

a.

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

b.

How many stereoisomers are formed from the reaction of cyclohexene with NBS?

How many stereoisomers are formed from the reaction of 3-methylcyclohexene with NBS?

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

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

(a)

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

(c)

A student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C₇H₁₁Br.

(a) Draw the resonance forms of the three possible allylic free radical intermediates.

(b) Rank these three intermediates from most stable to least stable.

(c) Draw the products obtained from each free-radical intermediate.

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.

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

(b)

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, cyclohexene undergoes the following light-promoted reaction:

a. Propose a mechanism for this 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 allylic halogenation reactions.

(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.

(a)