10. Addition Reactions

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?

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.]

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

(b)

For each of the products you predicted in Assessment 8.39, provide an arrow-pushing mechanism which rationalizes the formation of each product. Make sure your mechanism accounts for all products formed, including stereoisomers and regioisomers, where applicable.

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

a.

Each of the following reactions has two nucleophiles that could add to the intermediate formed by the reaction of the alkene with an electrophile. What is the major product of each reaction?

c.

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (iv) H₂SO₄ , H₂O

(b)

Which major product is formed in the acid-catalyzed hydration of ${\mathrm{CH}}_3$-${\mathrm{CH}}_2$-${\mathrm{CH}}_2$=${\mathrm{CH}}_2$ (3-methyl-1-butene)?

d. Is the reaction of 1-butene with HBr regioselective?

e. Is it stereoselective?

f. Is it stereospecific?

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?

Predict the product of the following reaction.

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?

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

e.

Draw the products of the following reactions. If the products can exist as stereoisomers, show which stereoisomers are formed

c. 1-ethylcyclohexene + H₂O + H₂SO₄

Predict the product(s) that would result when the following molecules are allowed to react under the following conditions: (vi) NaOH, H₂O . If there is no reaction, write 'no reaction.'

(a)