11. Radical Reactions

Which reagent system (HBr or HBr, H₂O₂) would you use to carry out the following transformations?

(a)

What five-carbon alkene forms the same product whether it reacts with HBr in the presence of a peroxide or with HBr in the absence of a peroxide?

Which reagent system (HBr or HBr, H₂O₂) would you use to carry out the following transformations?

(c)

Retrosynthetic analysis is the process of working backward to develop the synthesis of a new compound. In Chapter 10, we begin developing multistep syntheses in this manner. For now, try to work backward a single step by suggesting an alkene and a reagent that would give products (a)–(i). [Your answers should not include alkenes that undergo rearrangement to give the desired products.]

(d)

Provide the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HBr, H₂O₂

(c)

What alkyl halide will be obtained in greatest yield? Ignore stereoisomers.

f.

Provide an arrow-pushing mechanism that rationalizes the formation of each of the products you predicted in Assessment 8.35 (ii). Make sure your mechanism accounts for all products formed, including stereoisomers and regioisomers, where applicable.

What reagents are needed to carry out the following syntheses?

Provide the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HBr, H₂O₂.

(d)

Show how hex-1-yne might be converted to

a. 1,2-dichlorohex-1-ene.

b. 1-bromohex-1-ene.

c. 2-bromohex-1-ene.

Write the propagation steps for the addition of HBr to 1-methylcyclohexene in the presence of a peroxide

Provide the mechanism of the radical reactions shown.

(a)

Show how you would synthesize each compound using methylenecyclopentane as your starting material.

(b)

Which reagent system (HBr or HBr, H₂O₂) would you use to carry out the following transformations?

(b)