11. Radical Reactions

What hydrocarbon with the same molecular formula as in part a forms three monochlorinated products? One is achiral and two are chiral.

Explain why iodine (I₂) does not react with ethane, even though I₂ is more easily cleaved homolytically than the other halogens.

Write the initiation, propagation, and termination steps for the monochlorination of cyclohexane.

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

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?

Predict the major monohalogenation product(s) of the following reactions. Indicate whether you think the reaction will be selective and justify your position.

(c)

Predict the product(s) of the following halogenation reactions. Only one equivalent of the halogen is used in each case. If the reaction proceeds selectively, indicate this by only drawing the major product. If the reaction is not selective, draw all possible products.

(e)

Predict the product(s) of the following halogenation reactions. Only one equivalent of the halogen is used in each case. If the reaction proceeds selectively, indicate this by only drawing the major product. If the reaction is not selective, draw all possible products.

(f)

We have studied the following reactions in previous chapters. For each, (i) indicate which reaction sheets they should appear on, (ii) show the best structure to use to represent them, and (iii) write the notes you could put in the margin so that the mechanism is implied.

(b) Radical halogenation of an alkane

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

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

(a) Give an arrow-pushing mechanism, including the initiation step and two propagation steps.

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

(c)

Other molecules can be used as initiators in radical reactions. One such molecule is 2, 2'-azobisisobutyronitrile (AIBN). Show an arrow-pushing mechanism that rationalizes the formation of the following radical species. What are the driving forces of this reaction?

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.]

What alkane, with molecular formula C₅H₁₂, forms only one monochlorinated product when it is heated with Cl₂?