10. Addition Reactions

Provide a mechanism for the following reactions occurring with rearrangement.

(a) <IMAGE>

(•••) Cyclooctene is one of the smaller rings that can form a trans alkene. Would you expect cis-cyclooctene or trans-cyclooctene to react more quickly in an acid-catalyzed hydration reaction?

<IMAGE> <IMAGE>

trans-cyclooctene cis-cyclooctene

The mechanism of the acid-catalyzed hydration of an alkene to make an alcohol is shown. If this reaction is reversible, draw a mechanism that justifies formation of the alkene from the alcohol under similar conditions. How do you know this mechanism is correct?

<IMAGE>

Would you expect the following to produce an equal or unequal mixture of stereoisomers?

(b) <IMAGE>

Provide the expected product for the reaction of each of the following alkenes with H₂SO₄ and H₂O.

(d)

Provide the expected product for the reaction of each of the following alkenes with H₂SO₄ and H₂O.

(d) <IMAGE>

A chemist unsuccessfully attempted to produce the 1,4-cyclohexanediol by hydration of the cyclohexene shown.

(a) Provide a mechanism for the formation of the actual product.

(b) Suggest a pathway using acetyl chloride as a protecting group that will allow for the formation of the desired product.

<IMAGE>

(•••) LOOKING BACK The acid-catalyzed dehydration we learned in this chapter is reversible, as shown below. [We studied this reaction in Chapter 8.]

<IMAGE>

(d) How might you shift the equilibrium to the right?

When combining isoprene equivalents, IPP is never the electrophile. Why might this be? What is special about DPP that allows it to function better as an electrophile? [Draw the carbocation that each becomes.]

Suggest a mechanism for the synthesis of farnesol beginning with IPP and DPP.

<IMAGE>

farnesol

Provide the expected product for the reaction of each of the following alkenes with H₂SO₄ and H₂O.

(b) <IMAGE>

(•••) LOOKING BACK The acid-catalyzed dehydration we learned in this chapter is reversible, as shown below. [We studied this reaction in Chapter 8.]

<IMAGE>

(b) Without looking back, how do you know this mechanism is correct?

The pKa values of the carboxylic acid groups of oxaloacetic acid are 2.22 and 3.98.

b. The amount of hydrate present in an aqueous solution of oxaloacetic acid depends on the pH of the solution: 95% at pH 0, 81% at pH 1.3, 35% at pH 3.1, 13% at pH 4.7, 6% at pH 6.7, and 6% at pH 12.7. Explain this pH dependence.

<IMAGE>

How could the following compounds be prepared using an alkene as one of the starting materials?

c. <IMAGE>

How could the following compounds be prepared using an alkene as one of the starting materials?

e. <IMAGE>

Using any alkene and any other reagents, how would you prepare the following compounds?

e. <IMAGE>

Which compound is hydrated more rapidly?

<IMAGE>

Propose a mechanism for the following reaction:

<IMAGE>

Answer the following questions about the mechanism for the acid-catalyzed hydration of an alkene:

a. How many transition states are there?

b. How many intermediates are there?

c. Which step in the forward direction has the smallest rate constant?

What stereoisomers are obtained from each of the following reactions?

b. <IMAGE>

How could the following compounds be prepared using an alkene as one of the starting materials?

a. <IMAGE>

What is the major product of the reaction of 2-methyl-2-butene with each of the following reagents?

g. H2O + H2SO4

Propose a mechanism to show how 3,3-dimethylbut-1-ene reacts with dilute aqueous H2SO4 to give 2,3-dimethylbutan-2-ol and a small amount of 2,3-dimethylbut-2-ene.

HINT: When predicting products for electrophilic additions, first draw the structure of the carbocation (or other intermediate) that results from electrophilic attack.

Predict the products of the following hydration reactions.

b. 2−phenylpropene + dilute acid

c. 1-phenylcyclohexene + dilute acid

Propose mechanisms consistent with the following reactions.

b. <IMAGE>

Often, compounds can be synthesized by more than one method. Show how this 3° alcohol can be made from the

following:

<IMAGE>

(b) two different alkenes

When fumarate reacts with D2O in the presence of the enzyme fumarase, only one isomer of the product is formed, as shown here. Is the enzyme catalyzing a syn or an anti addition of D2O?

<IMAGE>