CHEM 2423

The carbon-carbon triple bond of an alkyne is composed of..?

• 3 sigma bonds

• 3 pi bonds

• 2 sigma bonds and 1 pi bonds

• 1 sigma bond, and 2 pi bonds

Which of the following tautomeric forms is more stable?

(a): H₃C-CH=O   ↔   (b): H₂C=C-OH

• a

• Both are equally stable

• b

• Both are unstable

Answer explanation

Select the incorrect statement regarding terminal alkynes.

• Terminal alkynes are not as acidic as alkanes

• Terminal alkynes are more acidic when compared with alkenes

• These have a replaceable acidic H atom

• Methylacetylene is an example of terminal alkynes

Which of the alkyne addition reactions below involve(s) an enol intermediate?

• A. Hydroboration/oxidation

• B. Treatment with HgSO4 in dilute H₂SO₄ 

• C. Hydrogenation

• Both A and B

• None of these

When CH3C≡CH (propyne) is treated with dilute H₂SO₄ in presence of HgSO₄ the major product will be:

• Propanol

• Propyl hydrogen sulphate

• Acetone

• Propanal

What kind of catalyst produces a cis-alkene?

• H₂ with NH₃

• H₂ with Lindlar catalyst

• H₂ with Pd/C

• Li/Na with NH₃

Oxidation Cleavage: CO₂ is formed by cleavage of what type of alkyne?

• A terminal alkyne

• An internal alkyne

• Both

In a reaction with an internal alkyne (R-C≡C-R), what reagents can form carboxylic acids (-COOH)?

• OH-/H₂O

• Li/Na

• KMNO₄/O₃

• Br/Cl

Which of the following is a way to synthesize alkynes?

• Elimination of alkyl halides

• Dehydrohalogenation of haloalkanes

• Elimination of alcohols

• All of these

What is the product obtained when a terminal alkyne undergoes hydroboration/oxidation? (Hint: This reaction is anti-Markovnikov)

• An aldehyde

  (-CHO)

• A methyl ketone (R-COCH₃)

• An enol

• An alkyne