Quiz - Alkynes - 3 | Alkynes

Organic Chemistry 2 - Quiz - Alkynes - 3


What influences the acidity of alkynes compared to other hydrocarbons?

The hybridization of the carbon atoms influencing the s-character leads to greater acidity in alkynes. The sp-hybridized carbons of alkynes have greater s-character and thus hold the electrons closer to the atom, stabilizing the negative charge better than sp2 or sp3 carbons.


Which method is least likely to be used in the industrial preparation of alkynes?

Direct addition of hydrogen to an alkyne is not a method for preparing alkynes, rather it is a reduction process that converts alkynes to alkanes. The other methods mentioned are legitimate preparation techniques for alkynes.


During the reduction of an alkyne to a cis-alkene, which catalyst should be employed?

Lindlar's catalyst is specifically used for the partial hydrogenation of alkynes to form cis-alkenes. It is a poisoned catalyst that prevents complete reduction to the alkane.


Which reagent would you use to prepare an alkyne from an alkene via halogenation followed by dehydrohalogenation?

To prepare an alkyne through halogenation and subsequent dehydrohalogenation from an alkene, all of the mentioned reagents would be used. The alkene is first halogenated with Cl2, and then dehydrohalogenated using a strong base like KOH or NaNH2.


When naming an alkyne with multiple substituents, what determines the direction of numbering?

Nomenclature rules prioritize giving multiple substituents, including the alkyne functional group, the lowest possible locants. This dictates the direction of numbering along the longest carbon chain.


In anti-Markovnikov addition of HBr to alkynes, what intermediate is predominantly formed?

In anti-Markovnikov addition of HBr using peroxides, a free-radical mechanism predominates forming a vinylic radical intermediate. This is due to the homolytic cleavage of the peroxide bond initiated by HBr.


Which statement about alkynes is false?

The chemical behavior of alkynes is not completely predictable by the Markovnikov rule. While some reactions follow this rule, others, like hydroboration-oxidation, follow anti-Markovnikov's rule.


The hydroboration-oxidation reaction of a terminal alkyne followed by aqueous workup produces what type of compound as the major product?

Hydroboration-oxidation of alkynes typically gives aldehydes as the major product when the reaction is carried out with a terminal alkyne, since the borane adds to the less hindered carbon, followed by oxidation to yield an aldehyde.