9. Alkenes and Alkynes

A student provided the product of the following reactions, but made a mistake. Identify the mistake, correct the mistake, and suggest a way for the student to avoid that mistake in the future.

(b)

Calculate for the following acid–base reactions. Which is the best base to use to deprotonate acetylene and make the acetylide anion?

(b) H₂N^- + H―C ≡ C―H ⇌ ^-C ≡ C―H + H₃N

A chemist is planning to synthesize 3-octyne by adding 1-bromobutane to the product obtained from the reaction of 1-butyne with sodium amide. Unfortunately, however, he forgot to order 1-butyne. How else can he prepare 3-octyne?

The introduction of elimination reactions provides a second way to synthesize alkynes in a two-step process starting with an alkene. Suggest a mechanism for both steps of this process.

Show the products of the following acetylide alkylation reactions. [Make sure your product has the correct number of carbons.]

(c)

What is the major product of the reaction of 1 mol of propyne with each of the following reagents?

i. sodium amide

Show the products of the following acetylide alkylation reactions. [Make sure your product has the correct number of carbons.]

(a)

In Chapter 10, you learned how to make an alkyne by acetylide alkylation with a 1° haloalkane. Suggest a mechanism by which this reaction occurs.

Show how you might synthesize the following compounds, using acetylene and any ­suitable alkyl halides as your starting materials. If the compound given cannot be ­synthesized by this method, explain why.

d. 4-methylhex-2-yne

e. 5-methylhex-2-yne

f. cyclodecyne

Predict the product of the following acetylide alkylations.

(a)

Predict the product of the following acetylide alkylations.

(c)

When the reaction scheme in Assessment 12.63 is done on a monosubstituted alkene, at least three equivalents of base are needed. Reacting the product of step 2 with D–Cl (D is an isotope of H) incorporates deuterium at the terminal carbon. Explain these two observations.

Suggest an acetylide ion and a carbonyl that might be used to make the following products.

(c) 5-phenylhex-2-yn-1-ol

Draw the product of each of the following reactions:

1.

Ethinylestradiol is a synthetic hormone mimic used as a contraceptive for its ability to prevent ovulation. Suggest a mechanism for the synthesis using sodium acetylide and estrone, followed by quenching with acid.