11. Radical Reactions

For the following reaction, answer questions (a)–(d).

(b) Which is the weakest bond in molecule A?

How many alkyl chlorides are obtained from monochlorination of the following alkanes? Disregard stereoisomers.

a.

Explain why free-radical halogenation usually gives mixtures of products.

For each reaction, show which stereoisomers are obtained

1. NBS/∆/peroxide

2. Br₂/CH₂Cl₂

A possible alternative mechanism to that shown in Problem 47 for the monochlorination of methane involves the following propagation steps:

How do you know that the reaction does not take place by this mechanism?

How many monochlorination products can be obtained from the radical chlorination of methylcyclohexane? Disregard stereoisomers.

Provide an arrow-pushing mechanism for the following alkane bromination. [Don't forget to use fishhook arrows to represent the movement of single electrons.]

When (1R,3S)-1-tert-butyl-1,3-dimethylcyclopentane is halogenated, one stereoisomer is produced in excess.

(b) explain why this reaction did not produce an equal mixture of stereoisomers.

A halogenation intended to make compound A formed B instead.

(c) Given the two mechanisms you drew, why might B have formed selectively?

How many alkyl chlorides are obtained from monochlorination of the following alkanes? Disregard stereoisomers.

h.

Using cyclohexane as one of your starting materials, show how you would synthesize the following compounds.

(a)

How many alkyl halides are obtained from monochlorination of the alkanes in Problem 4 if stereoisomers are included?

c.

What is the major product obtained from treating an excess of each of the following compounds with Cl₂ in the presence of ultraviolet light at room temperature? Disregard stereoisomers.

c.

For each alkane,

2. determine whether free-radical chlorination would be a good way to make any of these monochlorinated derivatives. Will the reaction give mostly one major product?

a. Cyclopentane

b. Methylcyclopentane

The following compounds have the same molecular formula as benzene. How many monobrominated products could each form?

1. HC≡CC≡CCH₂CH₃

2. CH₂=CHC≡CCH=CH₂