Читать книгу Organic Mechanisms - Xiaoping Sun - Страница 40

1 1.1 Dibenzylmercury (PhCH2)2Hg contains linear C─Hg─C bonds. At 140 °C the compound undergoes thermal decomposition to give 1,2‐diphenylethane PhCH2CH2Ph and mercury. Suggest a concerted mechanism and a stepwise mechanism for this reaction.

2 1.2 The following are two alternative mechanisms for the AlCl3 catalyzed Friedel–Crafts reaction of benzene with chloroethane. Show qualitative reaction profiles for both mechanisms. Which mechanism is more plausible? Explain.

3 1.3 The decomposition of bromoethane in gaseous phase to ethene and hydrogen bromide follows a first‐order rate law. Suggest a possible concerted and a stepwise mechanisms which are consistent with the rate law.

4 1.4 The rate of nitration of benzene in a mixture of nitric acid and sulfuric acid does not depend on the concentration of benzene. What conclusion can be drawn from this? Show qualitative energy profile for the stepwise reaction.

5 1.5 The mechanism for the autoxidation of hydrocarbons by oxygen is shown below:Apply the steady‐state approximation to work out the expected kinetics for the reaction.

6 1.6 For the SN1 solvolysis of the tertiary chloroalkanes R–Cl in ethanol at 25°C, the relative rates for three different chloroalkanes are 1, 1.2, and 18.4 for R = Me3C, tBuMe2C, and tBu2MeC, respectively. Is the difference due to electronic or steric effects? Explain. Draw qualitative energy profiles for the SN1 solvolysis of the three chloroalkanes.

7 1.7 For the following each pair of anions, compare their basicity and nucleophilicity. Account for the difference.(1) OH− and SH− (2) CH3COO− and C6H5COO−

8 1.8 Which of the following SN2 reactions goes faster? Explain by kinetic isotope effect.