Organic Chemistry Multiple Choice Questions on “Alkynes”.
1. Alkynes are more reactive than alkenes.
a) False
b) True
Answer: a
Clarification: Alkynes are not as reactive when compared with the alkenes and the alkanes as they even more unsaturated when compared with them.
2. Select the incorrect statement.
a) The addition reactions occur more frequently in the alkenes than the alkynes
b) The pi system of the alkynes gets weakened when they lose the pi atoms
c) Alkynes readily undergo oligomerization
d) Alkynes do not undergo polymerization
Answer: d
Clarification: Alkynes readily undergo polymerization and form polymers such as polyacetylenes.
3. Select the incorrect statement regarding terminal alkynes.
a) Methylacetylene is an example of terminal alkynes
b) Terminal alkynes are more acidic when compared with alkenes
c) Terminal alkynes are not as acidic as alkanes
d) These have a replaceable acidic hydrogen atom
Answer: c
Clarification: Terminal alkynes are very much acidic than both alkenes and alkanes as they have a high pKa value.
4. The major alkyne, acetylene compound is produced by which among the following application on natural gas?
a) Hydrogenation
b) Partial oxidation
c) Cracking
d) Hydrohalogenation
Answer: b
Clarification: A huge quantity of acetylene is produced by partial oxidation of the natural gas.
5. Majority of the alkynes are not prepared from/by ___________
a) Condensation
b) Acetylene
c) Dehydrohalogenation
d) Hydrogenation
Answer: d
Clarification: Often, alkynes are obtained from the acetylene through the condensation process and sometimes by dehydrohalogenation.
6. Alkynes cannot be prepared from ___________
a) Ketones
b) Alcohols
c) Aldehydes
d) Other alkynes
Answer: b
Clarification: Only the aldehydes, ketones, and few other alkynes can give rise to a new alkyne compound.
7. The transformation into carboxylic acids of the alkynes takes place with the help of which among the following reagents?
a) Potassium chlorate
b) Potassium permanganate
c) Potassium dichromate
d) Potassium chloride
Answer: b
Clarification: The cycloaddition of the alkynes leads to the oxidative cleavage among them and hence it results in the formation of carboxylic acids.
8. Identify the incorrect statement.
a) Alkynes exists in gaseous state
b) They are soluble in water
c) They are soluble in organic solvents
d) Alkynes have a very good boiling point
Answer: b
Clarification: Alkyne molecules being non-polar, they do not dissolve in polar solvents like water.
9. Which among the following alkynes is used as a rocket fuel?
a) Ethyne
b) Propyne
c) But-1-yne
d) Pent-1-yne
Answer: b
Clarification: Propyne has many advantages and it is not as hazardous as compared to the other fuels, so they are used in rocket fuels.
10. Which among the following product is formed when ethyne undergoes hydrogenation?
a) Formaldehyde
b) Formic acid
c) Acetaldehyde
d) Acetic acid
Answer: c
Clarification: When ethyne undergoes hydrogenation in the presence of sulphuric acid, it forms ethanal.