Lindlar's catalyst (Pd/BaSO\textsubscript{4} with quinoline)

Question 1

Which hybridization is found in the carbon atoms of an alkyne's triple bond, and what is the resulting molecular geometry?

Accepted Answer

sp hybridization; linear geometry

Question 2

What is the general formula for an alkyne, and how many elements of unsaturation does each triple bond contribute?

Accepted Answer

$$\mathrm{C}_n\mathrm{H}_{2n-2}$$; two elements of unsaturation

Question 3

Which of the following statements about terminal alkynes is correct?

Accepted Answer

Terminal alkynes can be deprotonated quantitatively by sodium amide ($$\mathrm{NaNH}_2).$$

Question 4

Which base is strong enough to deprotonate a terminal alkyne, forming an acetylide ion?

Accepted Answer

Sodium amide ($$\mathrm{NaNH}_2)$$

Question 5

In the SN2 reaction of an acetylide ion with an alkyl halide, which type of alkyl halide is most reactive?

Accepted Answer

Primary alkyl halide

Question 6

Which product is formed when pent-1-yne reacts with HBr in the presence of peroxides (ROOR)?

Accepted Answer

1-bromopent-1-ene (anti-Markovnikov product, mixture of E and Z isomers)

Question 7

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

Accepted Answer

Lindlar's catalyst (Pd/BaSO	extsubscript{4} with quinoline)

Question 8

What is the outcome when an internal alkyne is treated with sodium in liquid ammonia ($$\mathrm{Na}/\mathrm{NH}_3$$)?

Accepted Answer

A trans alkene is formed via anti addition

Question 9

Which of the following best describes the process of keto–enol tautomerism?

Accepted Answer

Interconversion between an enol and a ketone or aldehyde via proton transfer

Question 10

Which reagent is used for anti-Markovnikov hydration of a terminal alkyne, resulting in an aldehyde after tautomerization?

Accepted Answer

Disiamylborane followed by hydrogen peroxide and sodium hydroxide

Question 11

What is the product when pent-2-yne is treated with warm, basic potassium permanganate ($$\mathrm{KMnO}_4$$, KOH, heat)?

Accepted Answer

Acetic acid and propionic acid

Question 12

Which physical property is characteristic of alkynes with up to four carbons?

Accepted Answer

They are gases at room temperature

Question 13

Which statement about the bond lengths in ethane, ethene, and ethyne is correct?

Accepted Answer

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

Question 14

Which functional group has higher priority in IUPAC naming than an alkyne?

Accepted Answer

Alcohol

Question 15

What is the result of treating a vicinal dihalide with excess sodium amide ($$\mathrm{NaNH}_2) $$followed by water?

Accepted Answer

Formation of a terminal alkyne

Question 16

Which reaction is used to determine the position of a triple bond in an unknown alkyne?

Accepted Answer

Oxidative cleavage with potassium permanganate or ozonolysis

Question 17

Which product is formed when an acetylide ion attacks an aldehyde, followed by protonation?

Accepted Answer

Secondary alcohol

Question 18

What is the main difference between terminal and internal alkynes?

Accepted Answer

Terminal alkynes have an acetylinic hydrogen, internal alkynes do not.

Question 19

Which of the following is true about the addition of halogens (Cl	extsubscript{2} or Br	extsubscript{2}) to alkynes?

Accepted Answer

Both syn and anti addition occur, producing a mixture of cis and trans isomers.

ch 9 Alkynes: Structure, Properties, and Reactions

Study Guide - Practice Questions