Bromination of buta-1,3-diene with a single equivalent of Br₂ can give either of two products. (a) Which of these products (A or B) would you predict to be more stable? Justify your answer.

One way to think about concerted reactions is to imagine them as being stepwise reactions where, besides the slowest step, all others have infinitesimally small activation energies. Considering the hypothetical stepwise mechanism and actual concerted mechanism of epoxide formation, show what a reaction coordinate diagram might look like for each possibility.

(b) Concerted , actual mechanism (butterfly transition state:

Consider the Cope rearrangement, a reaction we describe in Chapter 20.

(a) Using the knowledge we have gained here in Chapter 9, suggest a one-step, concerted mechanism that explains the formation of B from A.

(b) Which side of the reaction would you expect to be favored? Justify your answer.

(c) Which product, A or B, would you expect to be hydrogenated with the more exothermic heat of hydrogenation?

One way to think about concerted reactions is to imagine them as being stepwise reactions where, besides the slowest step, all others have infinitesimally small activation energies. Considering the hypothetical stepwise mechanism and actual concerted mechanism of epoxide formation, show what a reaction coordinate diagram might look like for each possibility.

(a) Stepwise, hypothetical mechanism:

Bromination of a highly electron-rich alkene such as 2-methoxybut-2-ene has been shown to produce approximately equal mixtures of the trans- and cis-dibromide. Suggest an explanation for this observation.

In Chapter 19, we discuss the reaction of enols with bromine. This reaction produces α -bromoketones in good yields. Suggest a mechanism for this reaction and justify its deviation from the dibromide product you might have expected.

Predict the product of ozonolysis of the triglyceride shown.