Question 1

Which of the following statements best explains why sodium amide ($$\mathrm{$$NaNH_2$$}) is $$used to deprotonate terminal alkynes, but water is not suitable for this reaction?

Accepted Answer

The conjugate acid of sodium amide has a higher $$pK_a$$ than the terminal alkyne, making the deprotonation favorable.

Question 2

What is the major organic product when 1,2-dibromopentane is treated with excess $$\mathrm{$$NaNH_2$$} in $$liquid ammonia, followed by water?

Accepted Answer

2-Pentyne

Question 3

Which of the following alkyl halides would react most efficiently with a terminal alkynide anion in an $$\mathrm{S_N2}$$ alkylation reaction?

Accepted Answer

1-Bromopropane

Question 4

What is the product of the following reaction sequence?

$$\mathrm{CH_3CH_2C \equiv CH} \xrightarrow{1.\ $$NaNH_2$$ \, 2.\ CH_3CH_2I}$$

Accepted Answer

$$\mathrm{CH_3CH_2C \equiv CCH_2CH_3}$$

Question 5

Which catalyst is used to selectively hydrogenate an alkyne to a cis-alkene?

Accepted Answer

Lindlar's catalyst

Question 6

What is the expected product when 2-butyne is treated with sodium in liquid ammonia?

Accepted Answer

trans-2-Butene

Question 7

Which of the following best describes the regiochemistry of hydrohalogenation (addition of HX) to a terminal alkyne in the absence of peroxides?

Accepted Answer

Markovnikov addition

Question 8

A terminal alkyne reacts with $$\mathrm{HBr} in $$the presence of peroxides ($$\mathrm{ROOR}). $$What is the major product?

Accepted Answer

An anti-Markovnikov bromoalkene

Question 9

Which of the following reagents will convert a terminal alkyne to a methyl ketone via Markovnikov hydration?

Accepted Answer

$$\mathrm{H_2SO_4,\ H_2O,\ $$HgSO_4$$}$$

Question 10

What is the product when 1-hexyne is treated with $$\mathrm{1.\ BH_3$,\ THF\ 2.\ H_2O_2,\ NaOH}$$?

Accepted Answer

Hexanal

Question 11

Which of the following best describes the product(s) of ozonolysis of an internal alkyne?

Accepted Answer

Two carboxylic acids

Question 12

A terminal alkyne undergoes oxidative cleavage with $$\mathrm{1.\ O_3$,\ 2.\ H_2O}. $$What are the products?

Accepted Answer

One carboxylic acid and carbon dioxide

Question 13

Which of the following statements about the acidity of terminal alkynes is correct?

Accepted Answer

Terminal alkynes are more acidic than alkenes and alkanes.

Question 14

Which of the following best explains why alkynide anions react with methyl and primary alkyl halides but not with secondary or tertiary alkyl halides?

Accepted Answer

Secondary and tertiary alkyl halides undergo elimination rather than substitution due to steric hindrance.

Question 15

Which of the following reagents would you use to selectively reduce an alkyne to a trans-alkene?

Accepted Answer

Sodium in liquid ammonia

Question 16

What is the product of the complete hydrogenation of 2-pentyne using $$\mathrm{H_2$}$$ and $$\mathrm{Pt}$$?

Accepted Answer

Pentane

Question 17

Which of the following best describes the mechanism of halogenation (e.g., $$\mathrm{Br_2$}) of $$alkynes?

Accepted Answer

Anti addition via a halonium ion intermediate

Question 18

A student wants to synthesize 3-heptyne starting from acetylene. Which sequence of reagents would accomplish this?

Accepted Answer

1. $$\mathrm{$$NaNH_2$$}$$, 2. $$\mathrm{CH_3CH_2Br}$$, 3. $$\mathrm{$$NaNH_2$$}$$, 4. $$\mathrm{CH_3CH_2CH_2Br}$$

Alkynes: Structure, Reactivity, and Synthetic Transformations

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