Alkynes: An Introduction to Organic Synthesis

How would you prepare cis-2-butene starting from propyne, an alkyl halide, and any other reagents needed? This problem can’t be worked in a single step. You’ll have to carry out more than one reaction.

The following cycloalkyne is too unstable to exist. Explain

The final step in the hydration of an alkyne under acidic conditions is the tautomerization of an enol intermediate to give the corresponding ketone. The mechanism involves a protonation followed by a deprotonation.

Show the mechanism for each of the following tautomerizations.

There are seven isomeric alkynes with the formula ${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{10}}$ . Draw and name them.

What products would you expect from the following reactions?

b. 

What products would you expect from the following reactions?

a. ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\mathbf{\equiv }\mathbf{CH}\mathbf{+}{\mathbf{Cl}}_{\mathbf{2}}$

What products would you expect from the following reactions?

c. ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\mathbf{\equiv }{\mathbf{CCH}}_{\mathbf{3}}\mathbf{+}\mathbf{HBr}$

What products would you obtain by hydration of the following alkynes?

What alkynes would you start with to prepare the following ketones?

What alkyne would you start with to prepare each of the following compounds by a hydroboration–oxidation reaction?

Using any alkyne needed, how would you prepare the following alkenes? 

How would you prepare the following carbonyl compounds starting from an alkyne (reddish brown Br)?

How would you prepare the following carbonyl compounds starting from an alkyne (reddish-brown Br)?

b.

Using any alkyne needed, how would you prepare the following alkenes? 

 (b) cis-3-Heptene

Question:Using any alkyne needed, how would you prepare the following alkenes? 

(c) 3-Methyl-1-pentene

Using any alkyne needed, how would you prepare the following alkenes? 

(c) 3-Methyl-1-pentene

The of acetone, ${\mathbf{pk}}_{\mathbf{a}}$of acetone, ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{COCH}}_{\mathbf{3}}$ is 19.3. Which of the following bases is strong enough to deprotonate acetone?

(a) KOH  (pk_a of H₂O 15.7)

The pk_a of acetone, CH₃COCH₃, is 19.3. Which of the following bases is strong enough to deprotonate acetone?

(b) $\mathit{N}{\mathit{a}}^{\mathbf{+}}{\mathbf{ }}^{\mathbf{-}}\mathit{C}\mathbf{\equiv }\mathit{C}\mathit{H}$$\left({\mathrm{pk}}_a{H}_2{O}_{2 }\mathrm{of} 25\right)$

The pk_a of acetone, $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathit{C}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}$, is 19.3. Which of the following bases is strong enough to deprotonate acetone?

(c) $\mathit{N}\mathit{a}\mathit{H}\mathit{C}{\mathit{O}}_{\mathbf{3}}$($\mathit{p}{\mathit{k}}_{\mathbf{a}}$of H₂CO₃ 6.4)

The pk_a of acetone, CH₃COCH₃, is 19.3. Which of the following bases is strong enough to deprotonate acetone? 

(d) NaOCO₃ ( pk_a of CH₃OH 15.6)

Show the terminal alkyne and alkyl halide from which the following products can be obtained. If two routes look feasible, list both.

$\mathbf{a}\mathbf{.}\mathbf{ }{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\mathbf{\equiv }\mathbf{CH}$

Show the terminal alkyne and alkyl halide from which the following products can be obtained. If two routes look feasible, list both.

$\mathbf{b}\mathbf{.}\mathbf{ }{\left({\mathrm{CH}}_3\right)}_{\mathbf{2}}\mathbf{CHC}\mathbf{\equiv }{\mathbf{CCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}}$

Show the terminal alkyne and alkyl halide from which the following products can be obtained. If two routes look feasible, list both.

Which of the following bases could be used to deprotonate 1-butyne?

(a)

Which of the following bases could be used to deprotonate 1-butyne?

(c)

Which of the following bases could be used to deprotonate 1-butyne?

d)

Each of the following syntheses requires more than one step. How

would you carry them out?

(a)

(b)

Give IUPAC names for the following compounds:

Draw structures corresponding to the following names:

(a) 3,3-Dimethyl-4-octyne

(b) 3-Ethyl-5-methyl-1,6,8-decatriyne

(c) 2,2,5,5-Tetramethyl-3-hexyne

(d) 3,4-Dimethylcyclodecyne

(e) 3,5-Heptadien-1-yne

(f) 3-Chloro-4,4-dimethyl-1-nonen-6-yne

(g) 3-sec-Butyl-1-heptyne

(h) 5-tert-Butyl-2-methyl-3-octyne

Terminal alkynes react with and water to yield bromo ketones. For example:

Propose a mechanism for the reaction. To what reaction of alkenes is

the process analogous?

Propose structures for hydrocarbons that give the following products

on oxidative cleavage by KMnO₄ or O₃ :

Question: Identify the reagents a–c in the following scheme:

Let   be a group and assume that for each positive integer i , N_i  is a normal subgroup of G. If every element of   can be written uniquely in the form n_i1 .n_i2 ...n_ik with i₁ < i₂ < ... < i_k and n_ij$\in$N_ij , prove that G$\cong$$\sum _{\mathrm{i}=1}$ N_i   (see Exercise 34). [Hint: Adapt the proof of Theorem 9.1 by defining f(a₁, a₂...) to be the product of those a_i that are not the identity element.]

Question: How would you carry out the following conversions? More than one

step may be needed in some instances.

Question: How would you carry out the following reactions?

Question: Each of the following syntheses requires more than one step. How

would you carry them out?

(a) 

b)

How would you carry out the following transformation? More than one

step is needed.

How would you carry out the following conversions? More than one

step is needed in each case.

Synthesize the following compounds using 1-butyne as the only source of carbon along with any inorganic reagents you need. More than one step may be needed.(a) 1,1,2,2- Tetrachlorobutane(b) 1,1- Dichloro-2-ethylcyclopropane

How would you carry out the following reactions to introduce deuterium into organic molecules?

(a)

b. 

c. 

d.

The sex attractant given off by the common housefly is an alkene named muscalure. Propose a synthesis of muscalure starting from acetylene and any alkyl halides needed. What is the IUPAC name for muscalure?

Muscalure

A hydrocarbon of unknown structure has the formula C₈H₁₀. On catalytic hydrogenation over the Lindlar catalyst, 1 equivalent of H₂ is absorbed. On hydrogenation over a palladium catalyst, 3 equivalents of H₂ are absorbed.

(a) How many degrees of unsaturation are present in the unknown structure?

(b) How many triple bonds are present?

(c) How many double bonds are present?

(d) How many rings are present?

(e) Draw a structure that fits the data.

Occasionally, a chemist might need to invert the stereochemistry of an alkene—that is, to convert a cis alkene to a trans alkene, or vice versa. There is no one-step method for doing an alkene inversion, but the transformation can be carried out by combining several reactions in the proper sequence. How would you carry out the following reactions? 

(a) $\mathrm{tran}-5-\mathrm{decene}\stackrel{?}{\to }\mathbf{cis}\mathbf{-}\mathbf{5}\mathbf{-}\mathbf{decene}$

(b) $\mathrm{cis}-5-\mathrm{decene}\stackrel{?}{\to }\mathbf{trans}\mathbf{-}\mathbf{5}\mathbf{-}\mathbf{decene}$

The oral contraceptive agent Mestranol is synthesized using a carbonyl addition reaction like that shown in Problem 9-50. Draw the structure of the ketone needed.

1-Octen-3-ol, a potent mosquito attractant commonly used in mosquito traps, can be prepared in two steps from hexanal, ${\mathbf{CH}}_3{\mathbf{CH}}_2{\mathbf{CH}}_2{\mathbf{CH}}_2{\mathbf{CH}}_2\mathbf{CHO}$ . The first step is an acetylide-addition reaction like that described in Problem 9-50. What is the structure of the product from the first step, and how can it be converted into 1-octen-3-ol?

A cumulene is a compound with three adjacent double bonds. Draw an orbital picture of a cumulene. What kind of hybridization do the two central carbon atoms have? What is the geometric relationship of the substituents on one end to the substituents on the other end? What kind of isomerism is possible? Make a model to help see the answer.

${\mathbf{R}}_2\mathbf{C}\mathbf{=}\mathbf{C}\mathbf{=}\mathbf{C}\mathbf{=}{\mathbf{CR}}_2$

    A cumulene

Which of the following bases could be used to deprotonate 1-butyne?

(b) 

Arrange the carbocations below in order of increasing stability.