9. Alkenes and Alkynes

Predict the product of the multistep synthesis

a. How many alkenes could you treat with H₂, Pd/C to prepare methylcyclopentane?

b. Which of the alkenes is the most stable?

c. Which of the alkenes has the smallest heat of hydrogenation?

Predict the product of the following hydrogenation reactions run with a poisoned catalyst.

(a)

What reagents would you use for the following syntheses?

c. hexane from 3-hexyne

What stereoisomers are obtained from the following reactions?

b.

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ii) H₂, Pd/C, Pb(OAc)₂ , CaCO₃ (Lindlar's catalyst). If you expect two products, show both.

(c)

Show how you would accomplish the following synthetic transformations. Show all intermediates.

g. cyclodecyne → trans-cyclodecene

Predict the product of the following alkyne reductions.

(c)

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (iii) Na⁰ , NH₃ (liquid), ―33°C . If you expect two products, show both.

(c)

How can the following compounds be prepared using ethyne as the starting material?

f.

Which compound is formed when cyclohexene is reacted with $H_2$ in the presence of Pt catalyst?

The following reaction was recently reported to have been performed electrochemically.

(a) Identify the reagent and a solvent that could have been used if this reaction was done traditionally.

(b) What safety and environmental hazards are improved or worsened when doing this reaction electrochemically?

Reduction of an alkyne using the Lindlar catalyst, a reaction presented in Section 10.6.2, produces only the cis-alkene. Why?

What alkene would you start with if you wanted to synthesize

b. ethylcyclopentane?

In the hydrogenation of $1_{\text{decyne}}$ to $\text{decane}$, how many equivalents of ${H2}_{\text{gas}}$ are required for complete reduction?