Question 1

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

Accepted Answer

The sp-hybridized carbon in terminal alkynes has higher s character, stabilizing the negative charge on the conjugate base.

Question 2

What is the product when 1 mol of Br$$_2 is $$added to 1 mol of but-2-yne?

Accepted Answer

A mixture of cis- and trans-2,3-dibromobut-2-ene

Question 3

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

Accepted Answer

Lindlar's catalyst and H$$_2$$

Question 4

A student wants to synthesize 3-decyne from acetylene. Which sequence of reactions would achieve this?

Accepted Answer

Alkylate acetylene with ethyl bromide, then with hexyl bromide, using NaNH$$_2 as $$base.

Question 5

Which of the following best describes the product of hydration of a terminal alkyne using mercuric sulfate in aqueous sulfuric acid?

Accepted Answer

An enol intermediate that tautomerizes to a methyl ketone

Question 6

What is the major product when 1-hexyne is treated with excess HBr in the absence of peroxides?

Accepted Answer

1,1-dibromohexane

Question 7

Which of the following statements about the molecular geometry of acetylene (ethyne) is correct?

Accepted Answer

The molecule is linear due to sp hybridization of the carbon atoms.

Question 8

Which base is strong enough to quantitatively deprotonate a terminal alkyne?

Accepted Answer

NaNH$$_2$$

Question 9

What is the expected product when 2-butyne is treated with Na/NH$$_3 ($$liquid ammonia)?

Accepted Answer

trans-2-butene

Question 10

Which of the following is a correct retrosynthetic step for preparing a secondary alcohol from a terminal alkyne and an aldehyde?

Accepted Answer

React the acetylide ion (from the terminal alkyne) with the aldehyde, then protonate the alkoxide.

Question 11

Which of the following reactions will convert a vicinal dibromide to an alkyne?

Accepted Answer

Treatment with NaNH$$_2 at 150$$°C followed by water

Question 12

What is the product of hydroboration-oxidation of a terminal alkyne using (Sia)$$_2BH $$followed by H$$_2O$_2/$$NaOH?

Accepted Answer

An aldehyde

Question 13

Which of the following best describes the result of ozonolysis of an internal alkyne?

Accepted Answer

Two carboxylic acids

Question 14

A chemist wants to synthesize a substituted alkyne by $$S_N2$$ reaction. Which type of alkyl halide should be used for best results?

Accepted Answer

A primary alkyl halide

Question 15

Which of the following is true about the addition of HX (e.g., HBr) to a terminal alkyne in the presence of peroxides?

Accepted Answer

The addition is anti-Markovnikov, and the halide attaches to the least substituted carbon.

Question 16

Which of the following is a correct statement about the physical properties of alkynes?

Accepted Answer

Alkynes are nonpolar and insoluble in water.

Question 17

What is the major organic product when pent-2-yne is treated with dilute, neutral KMnO$$_4$$?

Accepted Answer

A diketone

Question 18

Which of the following is the correct IUPAC name for the compound CH$$_3C$	ext{≡}$$CCH$$_2CH$_3$$?

Accepted Answer

But-1-yne

Question 19

Which of the following best describes the bond lengths in ethyne (acetylene) compared to ethene and ethane?

Accepted Answer

The C–C bond in ethyne is shorter than in ethene and ethane.

Question 20

Which of the following is a correct application of retrosynthetic analysis in alkyne chemistry?

Accepted Answer

Identify the key carbon-carbon bond formation and work backwards from the product to suitable alkyl halides and acetylide ions.

Alkynes: Structure, Nomenclature, Properties, and Natural Occurrence

Study Guide - Practice Questions