$$\text{ethyne} \u003c \text{ethene} \u003c \text{ethane}$$

Two molecules of acetic acid ($$\text{CH}_3\text{COOH})$$

$$\text{C}\equiv\text{C} in an $$alkyne

Ethyne ($$\text{C}_2\text{H}_2)$$

Question 1

Which of the following statements best explains why terminal alkynes are more acidic than terminal alkenes?

Accepted Answer

Terminal alkynes have sp-hybridized carbons with higher s-character, which holds electrons closer to the nucleus and increases acidity.

Question 2

Arrange ethane, ethene, and ethyne in order of increasing C–C bond length.

Accepted Answer

$$	ext{ethyne} \u003c 	ext{ethene} \u003c 	ext{ethane}$$

Question 3

Which of the following bases is strong enough to completely deprotonate propyne?

Accepted Answer

$$	ext{NaNH}_2$$

Question 4

What is the molecular formula for a noncyclic alkyne with 5 carbon atoms?

Accepted Answer

$$	ext{C}_5	ext{H}_8$$

Question 5

Which alkyl halide will react fastest with the acetylide ion ($$	ext{HC}\equiv	ext{C}^-) in an SN2 $$reaction?

Accepted Answer

1-bromopropane

Question 6

Which product is formed when hex-1-yne undergoes catalytic hydrogenation with Lindlar’s catalyst?

Accepted Answer

hex-1-ene

Question 7

What is the product isolated from the treatment of 2-hexyne with sodium in liquid ammonia?

Accepted Answer

trans-hex-2-ene

Question 8

Which of the following is a limitation of alkylation of acetylide ions?

Accepted Answer

Only methyl and primary alkyl halides give good yields; secondary and tertiary halides undergo elimination.

Question 9

Which reagent is used to convert a geminal dihalide to a terminal alkyne?

Accepted Answer

$$	ext{NaNH}_2$$

Question 10

What is the product when 1-hexyne is treated with excess HCl?

Accepted Answer

1,1-dichlorohexane

Question 11

Which of the following reactions will produce a cis-alkene from an alkyne?

Accepted Answer

Catalytic hydrogenation with Lindlar’s catalyst

Question 12

What is the product of the acid-catalyzed hydration of 1-hexyne?

Accepted Answer

hexan-2-one

Question 13

Which of the following is the correct IUPAC name for HC≡CCH$$_2CH$_3$$?

Accepted Answer

but-1-yne

Question 14

Which product is formed when 2-butyne is subjected to ozonolysis followed by hydrolysis?

Accepted Answer

Two molecules of acetic acid ($$	ext{CH}_3	ext{COOH})$$

Question 15

Which of the following statements about the addition of hydrogen halides to terminal alkynes is correct?

Accepted Answer

The addition follows Markovnikov’s rule, with the halide attaching to the more substituted carbon.

Question 16

Which of the following is a product of hydroboration-oxidation of hex-1-yne?

Accepted Answer

hexanal

Question 17

Which of the following is true about the physical properties of alkynes?

Accepted Answer

Alkynes are nonpolar and insoluble in water.

Question 18

Which of the following bonds has the highest bond dissociation energy?

Accepted Answer

$$	ext{C}\equiv	ext{C} in an $$alkyne

Question 19

Which of the following compounds has a linear structure?

Accepted Answer

Ethyne ($$	ext{C}_2	ext{H}_2)$$

Chapter 9: Alkynes – Structure, Properties, Synthesis, and Reactions

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