10. Addition Reactions

Draw the mechanism for the reaction of cyclohexene with HCl

A student was about to turn in the products he had obtained from the reaction of HI with 3,3,3-trifluoropropene when he realized that the labels had fallen off his flasks and he did not know which label belonged to which flask. His friend reminded him of the rule that says the electrophile adds to the sp2 carbon bonded to the most hydrogens. In other words, he should label the flask containing the most product 1,1,1-trifluoro-2-iodopropane and label the flask containing the least amount of product 1,1,1-trifluoro-3-iodopropane. Should he follow his friend’s advice?

a. What product is obtained from the reaction of HCl with 1-butene? With 2-butene?

b. Which of the two reactions has the greater free energy of activation?

c. Which compound reacts more rapidly with HCl: (Z)-2-butene or (E)-2-butene?

Imagine an electrophilic addition where the first step is exothermic. Which carbocation—2° , 3° , or neither—would you expect to form preferentially? Explain.

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Provide a mechanism for the following reactions occurring with rearrangement.

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Using an excess of HCl in the following reaction resulted in a product that was not simply the substitution of chlorine for the hydroxyl group. Predict the identity of the product obtained.

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Provide an arrow-pushing mechanism that rationalizes the formation of each alkyl halide in Assessment 8.19.

Suggest an alkene that, upon reaction with the appropriate hydrohalic acid, will produce only the alkyl halide shown. [Ignore stereochemistry.]

Provide an arrow-pushing mechanism that rationalizes the formation of each of the products you predicted in Assessment 8.31. Make sure your mechanism accounts for all products formed, including stereoisomers and regioisomers, where applicable.

The following reaction gives two different constitutional isomers in nearly equal yields. Why doesn't this reaction produce only one product?

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(••) Which of the following alkenes would you expect to react fastest with HBr in each pair?

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A wayward chemist proposed the following mechanism for the addition of HBr to an alkene.

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(a) Why is this mechanism unlikely? (b) Compare the reaction coordinate diagrams for the actual mechanism studied in Section 8.3.1 and this alternate mechanism on the same graph.

What is the expected product for the reaction of each of the following alkenes with (i) HBr and (ii) HCl?

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a. Is the reaction of 2-butene with HBr regioselective?

b. Is it stereoselective?

c. Is it stereospecific?

What alkene should be used to synthesize each of the following alkyl bromides?

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Propose a mechanism for each of the following reactions:

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What is the major product obtained from the addition of HBr to the following compound?

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Which of the following compounds reacts with HBr more rapidly?

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Of the possible products shown for the following reaction, are there any that will not be formed?

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What alkene should be used to synthesize each of the following alkyl bromides?

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What alkene should be used to synthesize each of the following alkyl bromides?

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What is the major product obtained from the addition of HBr to each of the following compounds?

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b. <IMAGE>

What is the major product obtained from the addition of HBr to each of the following compounds?

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f. <IMAGE>

What will be the product of the preceding reaction if HBr is used in place of Br2?

What stereoisomers are obtained from the following reactions?

c. (E)-3-methyl-2-pentene + HBr

d. cis-3-hexene + HBr

What is the major product of the reaction of each of the following with HBr?

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b. When 1-chlorocyclohexene reacts with HBr, the major product is 1-bromo-1-chlorocyclohexane.

Propose a mechanism for this reaction, and explain why your proposed intermediate is more stable than the other possible intermediate

Propose mechanisms consistent with the following reactions.

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(a) Based on what you know about the relative stabilities of alkyl cations and benzylic cations, predict the product of addition of HBr to 1-phenylpropene.

(b) Propose a mechanism for this reaction.

Show how hex-1-yne might be converted to

e. 2-bromohexane.

Limonene is one of the compounds that give lemons their tangy odor. Show the structures of the products expected when limonene reacts with an excess of each of these reagents.

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i. hydrogen bromide gas in a solution containing dimethyl peroxide

When 3-methyl-1-butene reacts with HBr, two alkyl halides are formed: 2-bromo-3-methylbutane and 2-bromo-2-methylbutane. Propose a mechanism

that explains the formation of these two products.