11. Radical Reactions

Use the information in Table 4-2 (p. 167) to rank the following radicals in decreasing order of stability.

Use the information in Table 4-2 to explain why toluene (PhCH₃) has a very high octane rating of 111. Write an equation to show how toluene reacts with an alkyl free radical to give a relatively stable radical.

A student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C₇H₁₁Br.

b. Rank these three intermediates from most stable to least stable.

Explain the dramatic difference in rotational energy barriers of the following three alkenes. (Hint: Consider what the transition states must look like.)

The following ethers are ranked according to their ability to form explosive peroxides. Explain this ranking based on your knowledge of the reaction mechanism.

Based on the stability of the radicals produced, predict which bond in each pair would have the higher bond-dissociation energy.

(a)

Based on the stability of the radicals produced, predict which bond in each pair would have the higher bond-dissociation energy.

(b)

Based on the stability of the radicals produced, predict which bond in each pair would have the higher bond-dissociation energy.

(c)

Why is a 2° carbon radical more stable than a 1° carbon radical?

The following polyunsaturated fat, which does not exist in nature, is oxidized at a rate similar to oleic acid (Table 11.14), despite having two cis-alkenes. Why?

Ethers can be converted into radicals, some more easily than others. Which of the following radicals is more stable, and thus, more likely to form?

Based on the stability of the radicals produced, predict which bond in each pair would have the higher bond-dissociation energy.

(d)

Methyl t-butyl ether (MTBE) is used preferentially over diethyl ether because it is less prone to form peroxides. Explain this observation in terms of the two structures.

a. Which of the hydrogens in the structure in the margin is the easiest for a chlorine radical to remove?

b. How many secondary hydrogens does the structure have?

Rank the following radicals in decreasing order of stability. Classify each as primary, secondary, or tertiary.

a. The isopentyl radical,

b. The 3-methyl-2-butyl radical,

c. The 2-methyl-2-butyl radical,

d.