(a) Draw a reaction-energy diagram for the following reaction: The activation energy is

Draw Lewis structures for the following free radicals. (a) The ethyl radical, (b) The tert-butyl radical, (c) The isopropyl radical (2-propyl radical) (d) The iodine atom

(a) Write the propagation steps leading to the formation of dichloromethane from chloromethane. (b) Explain why free-radical halogenation usually gives mixtures of products. (c) How could an industrial plant control the proportions of methane and chlorine to favor production of To favor CH CCl4? 3Cl?

Each of the following proposed mechanisms for the free-radical chlorination of methane is wrong. Explain how the experimental evidence disproves each mechanism.

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?

The following reaction has a value of (a) Calculate at room temperature (25 C) for this reaction as written. (b) Starting with a 1 M solution of and calculate the final concentrations of all four species at equilibrium.

Under base-catalyzed conditions, two molecules of acetone can condense to form diacetone alcohol. At room temperature (25 C), about 5% of the acetone is converted to diacetone alcohol. Determine the value of for this reaction.

When ethene is mixed with hydrogen in the presence of a platinum catalyst, hydrogen adds across the double bond to form ethane. At room temperature, the reaction goes to completion. Predict the signs of and for this reaction. Explain these signs in terms of bonding and freedom of motion

For each reaction, estimate whether for the reaction is positive, negative, or impossible to predict. (a) (catalytic cracking) (b) The formation of diacetone alcohol: C10H22 heat catalyst " C3H6 + C7H16 n-decane propene heptane S Problem-solving Hint In general, two smaller molecules (or fragments, such as radicals) have more freedom of motion (greater entropy) than one larger molecule. H H H H C C Pt catalyst ethene + H2 H C H H C H H H ethane OH O O OH 2 CH3 C CH3 CH3 C CH2 C(CH3)2 (c) + O CH3OH H+ + H

For each reaction, estimate whether for the reaction is positive, negative, or impossible to predict. (a) (catalytic cracking) (b) The formation of diacetone alcohol: C10H22 heat catalyst " C3H6 + C7H16 n-decane propene heptane S Problem-solving Hint In general, two smaller molecules (or fragments, such as radicals) have more freedom of motion (greater entropy) than one larger molecule. H H H H C C Pt catalyst ethene + H2 H C H H C H H H ethane OH O O OH 2 CH3 C CH3 CH3 C CH2 C(CH3)2 (c) + O CH3OH H+ + H

(a) Using bond-dissociation enthalpies from Table 4-2 (page 143), calculate the heat of reaction for each step in the free-radical bromination of methane. (b) Calculate the overall heat of reaction.

The reaction of tert-butyl chloride with methanol is found to follow the rate equation (a) What is the kinetic order with respect to tert-butyl chloride? (b) What is the kinetic order with respect to methanol? (c) What is the kinetic order overall?

Under certain conditions, the bromination of cyclohexene follows an unusual rate law: rate = kr[cyclohexene][Br2] 2 H H H H Br Br Br + 2 (a) What is the kinetic order with respect to cyclohexene? (b) What is the kinetic order with respect to bromine? (c) What is the overall kinetic order?

When a small piece of platinum is added to a mixture of ethene and hydrogen, the following reaction occurs: H H H H C C Pt catalyst ethene + H2 H C H H C H H H ethane hydrogen

(a) Draw the reaction-energy diagram for the reverse reaction: (b) What is the activation energy for this reverse reaction? (c) What is the heat of reaction for this reverse reaction?

(a) Draw a reaction-energy diagram for the following reaction: The activation energy is 4 kJ mol (1 kcal mol), and the overall for the reaction is (b) Give the equation for the reverse reaction. (c) What is the activation energy for the reverse reaction?

The bromination of methane proceeds through the following steps: (a) Draw a complete reaction-energy diagram for this reaction. (b) Label the rate-limiting step. (c) Draw the structure of each transition state. (d) Compute the overall value of for the bromination.

(a) Using the BDEs in Table 4-2 (p. 143), compute the value of for each step in the iodination of methane. (b) Compute the overall value of for iodination. (c) Suggest two reasons why iodine does not react well with methane.

What would be the product ratio in the chlorination of propane if all the hydrogens were abstracted at equal rates?

Classify each hydrogen atom in the following compounds as primary (1), secondary (2), or tertiary (3). (a) butane (b) isobutane (c) 2-methylbutane (d) cyclohexane (e) norbornane (bicyclo[2.2.1]heptane)

Use the bond-dissociation enthalpies in Table 4-2 (page 143) to calculate the heats of reaction for the two possible first propagation steps in the chlorination of isobutane. Use this information to draw a reaction-energy diagram like Figure 4-8, comparing the activation energies for formation of the two radicals.

Predict the ratios of products that result from chlorination of isopentane (2-methylbutane).

(a) When n-heptane burns in a gasoline engine, the combustion process takes place too quickly. The explosive detonation makes a noise called knocking. When 2,2,4-trimethylpentane (isooctane) is burned, combustion takes place in a slower, more controlled manner. Combustion is a free-radical chain reaction, and its rate depends on the reactivity of the free-radical intermediates. Explain why isooctane has less tendency to knock than does n-heptane. (b) Alkoxy radicals are generally more stable than alkyl radicals. Write an equation showing an alkyl free radical (from burning gasoline) abstracting a hydrogen atom from tert-butyl alcohol, Explain why tert-butyl alcohol works as an antiknock additive for gasoline. (c) Use the information in Table 4-2 (page 143) 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) Compute the heats of reaction for abstraction of a primary hydrogen and a secondary hydrogen from propane by a fluorine radical. (b) How selective do you expect free-radical fluorination to be? (c) What product distribution would you expect to obtain from the free-radical fluorination of propane?

2,3-Dimethylbutane reacts with bromine in the presence of light to give a monobrominated product. Further reaction gives a good yield of a dibrominated product. Predict the structures of these products, and propose a mechanism for the formation of the monobrominated product.

In the presence of a small amount of bromine, cyclohexene undergoes the following lightpromoted reaction: (a) Propose a mechanism for this reaction. (b) Draw the structure of the rate-limiting transition state

Draw resonance forms to show how the BHA radical is stabilized by delocalization of the radical electron over other atoms in the molecule.

Write an equation for the reaction of vitamin E with an oxidizing radical to give ROH and a less reactive free radica

The triphenylmethyl cation is so stable that some of its salts can be stored for months. Explain why this cation is so stable.

Rank the following carbocations in decreasing order of stability. Classify each as primary, secondary, or tertiary. (a) The isopentyl cation, (b) The 3-methyl-2-butyl cation, (c) The 2-methyl-2-butyl cation, CH3C + 1CH32CH2CH

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, CH3C1CH32CH2CH3

Acetylacetone (pentane-2,4-dione) reacts with sodium hydroxide to give water and the sodium salt of a carbanion. Write a complete structural formula for the carbanion, and use resonance forms to show the stabilization of the carbanion.

Acetonitrile is deprotonated by very strong bases. Write resonance forms to show the stabilization of the carbanion that results

When it is strongly heated, ethyl diazoacetate decomposes to give nitrogen gas and a carbene. Draw a Lewis structure of the carbene

The following reaction is a common synthesis used in the organic chemistry laboratory course. When we double the concentration of methoxide ion (CH3O-), we find that the reaction rate doubles. When we triple the concentration of 1-bromobutane, we find that the reaction rate triples. (a) What is the order of this reaction with respect to 1-bromobutane? What is the order with respect to methoxide ion? Write the rate equation for this reaction. What is the overall order? (b) One lab textbook recommends forming the sodium methoxide in methanol solvent, but before adding 1-bromobutane, they first distill off enough methanol to reduce the mixture to half of its original volume. What difference in rate will we see when we run the reaction (using the same amounts of reagents) in half the volume of solvent?

Consider the following reaction-energy diagram

Draw a reaction-energy diagram for a one-step exothermic reaction. Label the parts that represent the reactants, products, transition state, activation energy, and heat of reaction

Draw a reaction-energy diagram for a two-step endothermic reaction with a rate-limiting second step

Draw a reaction-energy diagram for a two-step endothermic reaction with a rate-limiting second step

Label each hydrogen atom in the following compounds as primary (1), secondary (2), or tertiary (3). (a) (b) (c) CH3CH2CH1CH322 1CH323CCH2CH3 1CH322CHCH1CH32CH2CH3

Use bond-dissociation enthalpies (Table 4-2, p. 143) to calculate values of for the following reactions.

Use the information in Table 4-2 (p. 143) to rank the following radicals in decreasing order of stability

For each alkane, 1. Draw all the possible monochlorinated derivatives. 2. Determine whether free-radical chlorination would be a good way to make any of these monochlorinated derivatives. (Will the reaction give mostly one major product?) 3. Which monobrominated derivatives could you form in good yield by free-radical bromination? (a) cyclopentane (b) methylcyclopentane (c) 2-methylpentane (d) 2,2,3,3-tetramethylbutane

For each alkane, 1. Draw all the possible monochlorinated derivatives. 2. Determine whether free-radical chlorination would be a good way to make any of these monochlorinated derivatives. (Will the reaction give mostly one major product?) 3. Which monobrominated derivatives could you form in good yield by free-radical bromination? (a) cyclopentane (b) methylcyclopentane (c) 2-methylpentane (d) 2,2,3,3-tetramethylbutane

Draw the important resonance forms of the following free radicals.

In the presence of a small amount of bromine, the following light-promoted reaction has been observed

For each compound, predict the major product of free-radical bromination. Remember that bromination is highly selective, and only the most stable radical will be formed. (a) cyclohexane (b) methylcyclopentane (c) decalin (d) hexane

When exactly 1 mole of methane is mixed with exactly 1 mole of chlorine and light is shone on the mixture, a chlorination reaction occurs. The products are found to contain substantial amounts of di-, tri-, and tetrachloromethane, as well as unreacted methane. (a) Explain how a mixture is formed from this stoichiometric mixture of reactants, and propose mechanisms for the formation of these compounds from chloromethane. (b) How would you run this reaction to get a good conversion of methane to Of methane

The chlorination of pentane gives a mixture of three monochlorinated products. (a) Draw their structures. (b) Predict the ratios in which these monochlorination products will be formed, remembering that a chlorine atom abstracts a secondary hydrogen about 4.5 times as fast as it abstracts a primary hydrogen.

(a) Draw the structure of the transition state for the second propagation step in the chlorination of methane. Show whether the transition state is product-like or reactant-like, and which of the two partial bonds is stronger. (b) Repeat for the second propagation step in the bromination of methane.

Peroxides are often added to free-radical reactions as initiators because the oxygenoxygen bond cleaves homolytically rather easily. For example, the bond-dissociation enthalpy of the bond in hydrogen peroxide is only 213 kJ mol (51 kcal mol). Give a mechanism for the hydrogen peroxide-initiated reaction of cyclopentane with chlorine. The BDE for HO Cl is 210 kJ mol (50 kcal/mol).

When dichloromethane is treated with strong NaOH, an intermediate is generated that reacts like a carbene. Draw the structure of this reactive intermediate, and propose a mechanism for its formation

When ethene is treated in a calorimeter with and a Pt catalyst, the heat of reaction is found to be and the reaction goes to completion. When the reaction takes place at 1400 K, the equilibrium is found to be evenly balanced, with Compute the value of for this reaction

When a small amount of iodine is added to a mixture of chlorine and methane, it prevents chlorination from occurring. Therefore, iodine is a free-radical inhibitor for this reaction. Calculate values for the possible reactions of iodine with species present in the chlorination of methane, and use these values to explain why iodine inhibits the reaction. (The bond-dissociation enthalpy is 211 kJ mol or 50 kcal mol.)

Tributyltin hydride is used synthetically to reduce alkyl halides, replacing a halogen atom with hydrogen. Freeradical initiators promote this reaction, and free-radical inhibitors are known to slow it or stop it. Your job is to develop a mechanism, using the following reaction as the example.

When healthy, Earths stratosphere contains a low concentration of ozone that absorbs potentially harmful ultraviolet (UV) radiation by the cycle shown at right. Chlorofluorocarbon refrigerants, such as Freon 12 are stable in the lower atmosphere, but in the stratosphere they absorb high-energy UV radiation to generate chlorine radicals. The presence of a small number of chlorine radicals appears to lower ozone concentrations dramatically. The following reactions are all known to be exothermic (except the one requiring light) and to have high rate constants. Propose two mechanisms to explain how a small number of chlorine radicals can destroy large numbers of ozone molecules. Which of the two mechanisms is more likely when the concentration of chlorine atoms is very small?

When healthy, Earths stratosphere contains a low concentration of ozone that absorbs potentially harmful ultraviolet (UV) radiation by the cycle shown at right. Chlorofluorocarbon refrigerants, such as Freon 12 are stable in the lower atmosphere, but in the stratosphere they absorb high-energy UV radiation to generate chlorine radicals. The presence of a small number of chlorine radicals appears to lower ozone concentrations dramatically. The following reactions are all known to be exothermic (except the one requiring light) and to have high rate constants. Propose two mechanisms to explain how a small number of chlorine radicals can destroy large numbers of ozone molecules. Which of the two mechanisms is more likely when the concentration of chlorine atoms is very small?

Iodination of alkanes using iodine (I2) is usually an unfavorable reaction. (See Problem 4-17, for example.) Tetraiodomethane (CI4) can be used as the iodine source for iodination, in the presence of a free-radical initiator such as hydrogen peroxide. Propose a mechanism (involving mildly exothermic propagation steps) for the following proposed reaction. Calculate the value of for each of the steps in your proposed mechanism.