Question 1

Which of the following statements best explains why internal alkynes are more stable than terminal alkynes?

Accepted Answer

Internal alkynes have more alkyl groups, which stabilize the triple bond through hyperconjugation and electron donation.

Question 2

What is the correct IUPAC name for the following compound: $$\mathrm{CH_3CH_2C \equiv CCH_2CH_3}$$?

Accepted Answer

Hex-3-yne

Question 3

Which of the following best describes the hybridization and geometry of the carbons in the triple bond of an alkyne?

Accepted Answer

sp hybridized, linear geometry

Question 4

Which reagent would you use to selectively hydrogenate an alkyne to a cis-alkene without further reduction to an alkane?

Accepted Answer

$$\mathrm{H_2$}$$, Lindlar catalyst

Question 5

A terminal alkyne reacts with sodium amide ($$\mathrm{$$NaNH_2$$}) $$followed by an alkyl halide. What is the role of sodium amide in this reaction?

Accepted Answer

It deprotonates the terminal alkyne to form an acetylide ion.

Question 6

Which product is formed when 2-butyne reacts with excess bromine ($$\mathrm{Br_2$}$$)?

Accepted Answer

1,1,2,2-tetrabromobutane

Question 7

Which of the following statements about the addition of water to alkynes is correct?

Accepted Answer

The initial product is an enol, which rapidly tautomerizes to a ketone.

Question 8

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

Accepted Answer

Hexanal

Question 9

Which of the following best explains why alkynes are more acidic than alkenes or alkanes?

Accepted Answer

The sp-hybridized carbon in alkynes holds the negative charge more effectively due to higher s-character.

Question 10

Which sequence of reagents would convert 1-pentyne to trans-2-pentene?

Accepted Answer

$$\mathrm{Na}$$, $$\mathrm{NH_3$} (l)$$

Question 11

When 2-methyl-3-hexyne is treated with excess $$\mathrm{HBr}$$, what is the major product?

Accepted Answer

3,3-dibromo-2-methylhexane

Question 12

Which of the following is a correct retrosynthetic step for preparing 1-butyne from ethyne ($$\mathrm{HC \equiv CH}$$)?

Accepted Answer

React ethyne with $$\mathrm{$$NaNH_2$$}$$, then with ethyl bromide ($$\mathrm{C_2H_5Br})$$

Question 13

Which of the following best describes the product of the hydration of a terminal alkyne using $$\mathrm{$$HgSO_4$$}$$, $$\mathrm{H_2SO_4}$$, and $$\mathrm{H_2O}$$?

Accepted Answer

A methyl ketone

Question 14

Which of the following is the correct order of stability for the following cations: tertiary carbocation, secondary vinylic cation, methyl carbocation, vinylic cation?

Accepted Answer

Tertiary carbocation \u003e methyl carbocation \u003e secondary vinylic cation \u003e vinylic cation

Question 15

Which of the following reactions would produce a trans-alkene from an alkyne?

Accepted Answer

Dissolving metal reduction with $$\mathrm{Na} in$$ $$\mathrm{NH_3$} (l)$$

Question 16

Which of the following best describes the product(s) when 1-hexyne is treated with excess $$\mathrm{Br_2$}$$?

Accepted Answer

1,1,2,2-tetrabromohexane

Question 17

Which of the following is the correct IUPAC name for a molecule with the structure $$\mathrm{CH_3CH_2C \equiv CCH_2CH_2CH_3}$$?

Accepted Answer

Hept-3-yne

Question 18

Which of the following statements about the hydroboration-oxidation of alkynes is correct?

Accepted Answer

Terminal alkynes give aldehydes, while internal alkynes give ketones.

Chapter 10: Alkynes – Properties, Nomenclature, Reactions, and Synthesis

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