Question 1

Which of the following statements best explains why the C-H bond in ethyne (acetylene) is more acidic than the C-H bond in ethene or ethane?

Accepted Answer

The sp hybridized carbon in ethyne holds electrons closer, stabilizing the negative charge on the conjugate base.

Question 2

What is the product of the complete catalytic hydrogenation of 2-butyne using H2 and Pd/C?

Accepted Answer

Butane

Question 3

Which reagent would you use to selectively reduce an alkyne to a cis-alkene?

Accepted Answer

Lindlar's catalyst

Question 4

A terminal alkyne is treated with NaNH2 followed by a primary alkyl bromide. What is the major product?

Accepted Answer

An internal alkyne with a new carbon-carbon bond at the terminal position

Question 5

Which of the following best describes the product of hydration of a terminal alkyne using $\mathrm{HgSO_4}$, $\mathrm{H_2SO_4}$, and water?

Accepted Answer

A methyl ketone via Markovnikov addition

Question 6

Which of the following reactions will convert a terminal alkyne into a trans-alkene?

Accepted Answer

Na in liquid $\mathrm{NH_3}$

Question 7

What is the major organic product when 1-hexyne is treated with $\mathrm{(Sia)_2BH}$ followed by $\mathrm{H_2O_2}$ and $\mathrm{OH^-}$?

Accepted Answer

Hexanal

Question 8

Which of the following best explains why the addition of HX to an alkyne is slower than to an alkene?

Accepted Answer

The alkyne's electrons are held closer to the nucleus, making it less nucleophilic.

Question 9

What is the product of ozonolysis of 2-pentyne?

Accepted Answer

Propanoic acid and acetic acid

Question 10

Which of the following bases is strong enough to deprotonate a terminal alkyne?

Accepted Answer

Sodium amide ($\mathrm{NaNH_2}$)

Question 11

Which product is formed when 1-hexyne reacts with excess $\mathrm{Br_2}$ in $\mathrm{CCl_4}$?

Accepted Answer

Tetrabromohexane

Question 12

Which of the following statements about the addition of HBr to alkynes in the presence of peroxides is correct?

Accepted Answer

The product is formed via anti-Markovnikov addition.

Question 13

What is the IUPAC name for the following compound: $\mathrm{CH_3C \equiv CCH_2CH_3}$?

Accepted Answer

2-Pentyne

Question 14

Which of the following is a correct statement about the thermodynamics of enol-keto tautomerization?

Accepted Answer

The keto form is generally more stable due to stronger C=O bonds.

Question 15

Which of the following best describes the mechanism when a terminal alkyne reacts with an epoxide under basic conditions?

Accepted Answer

The acetylide anion attacks the less substituted carbon of the epoxide via an $\mathrm{S_N2}$ mechanism.

Question 16

Which of the following is the correct order of acidity (most to least acidic) for the following compounds: ethyne, ethene, ethane?

Accepted Answer

$\mathrm{HC \equiv CH > H_2C=CH_2 > H_3C-CH_3}$

Question 17

Which of the following statements about the addition of $\mathrm{X_2}$ (e.g., Br2) to alkynes is correct?

Accepted Answer

The reaction proceeds via a bridged halonium ion intermediate.

Question 18

Which of the following best describes the product of hydroboration-oxidation of a terminal alkyne?

Accepted Answer

An aldehyde via anti-Markovnikov addition

Question 19

Which of the following is a key difference between the reduction of alkynes with Lindlar's catalyst and with sodium in liquid ammonia?

Accepted Answer

Lindlar's catalyst gives a cis-alkene, while sodium in liquid ammonia gives a trans-alkene.

Comprehensive Study Notes on Alkynes: Structure, Properties, and Reactions

Study Guide - Practice Questions