11. Radical Reactions

If a small amount of a moderately nonpolar poisonous compound was added to a pond, why would it be safer to drink the water than it would be to eat the fish that live there?

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

h.

Show how free-radical halogenation might be used to synthesize the following ­compounds. In each case, explain why we expect to get a single major product.

(a) 1-chloro-2,2-dimethylpropane (neopentyl chloride)

(b) 2-bromo-2-methylbutane

The radical fluorination of 2-methyl propane resulted in a 14:86 ratio of products.

(b) From the relative reactivity, calculate the difference in energy between the transition states of the first propagation steps leading to a 1° and 3° radical.

Free-radical chlorination of hexane gives very poor yields of 1-chlorohexane, while cyclohexane can be converted to chlorocyclohexane in good yield.

a. How do you account for this difference?

b. What ratio of reactants (cyclohexane and chlorine) would you use for the synthesis of chlorocyclohexane?

Write the propagation steps leading to the formation of dichloromethane (CH₂Cl₂) from chloromethane.

For each alkane,

1. draw all the possible monochlorinated derivatives.

a. Cyclopentane

b. Methylcyclopentane

Predict the major products of the following alkane halogenation reactions. [The number of products shown ignores the formation of racemic mixtures.]

(d)

Cyclizations can be carried out under radical conditions involving Bu₃SnH and a catalytic amount of AIBN. Suggest a mechanism for this reaction. [Pay close attention to the bonds formed and broken in developing your mechanism. It may be helpful to number the carbons.]

For each alkane,

1. draw all the possible monochlorinated derivatives.

c. 2-methylpentane

d. 2,2,3,3-tetramethyl butane

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

a.

Write a mechanism for the light-initiated reaction of cyclohexane with chlorine to give chlorocyclohexane. Label the ­initiation and propagation steps.

Provide a mechanism for the chlorination of cyclohexane. Be sure to include initiation, propagation, and three possible termination steps.

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.

a.