This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Alkenes”.
1. In Alkenes the Carbon atoms are connected to each other by a ___________
a) Single bond
b) Double bond
c) Triple bond
d) Not connected
View Answer
Explanation: Alkenes have at least one double bond in addition to single bond as they are unsaturated hydrocarbons.
2. Which among these is not a structural isomer of the compound C4H8?
a) But-1-ene
b) But-2-ene
c) But-3-ene
d) 2-methylpropene
View Answer
Explanation: The compound but-3-ene have a structural formula different from the above three and hence it is not a structural isomer of C4H8.
3. Select the incorrect statement regarding alkenes.
a) In alkenes, the carbons are connected by pi bonds
b) Alkenes have almost same physical properties as that of the alkanes
c) Alkenes are less reactive than alkanes
d) Alkenes undergo polymerization reaction
View Answer
Explanation: Alkenes are not less reactive than alkanes, indeed they are very reactive compared with them due to the presence of C=C.
4. Identify the addition reaction which is not undergone by the alkenes?
a) Mercuration
b) Oxymercuration
c) Hydroboration
d) Halogenation
View Answer
Explanation: Alkenes do not undergo mercuration, indeed they undergo oxymercuration , a process in which an alkene is converted into an alcohol.
5. Identify the incorrect statement regarding the synthesis of alkenes.
a) Cracking of a hydrocarbon yields alkenes
b) The reactions are exothermic
c) Zeolite catalyst helps in the synthesis of alkenes
d) The synthesis of alkenes is otherwise known as reforming
View Answer
Explanation: The reactions takes place at high temperatures and hence they are endothermic.
6. Identify the one which shows E-Z mechanism?
a) 3-methylpent-2-ene
b) 2-methylpent-2-ene
c) Methyl-3-pent-2-ene
d) 2,3-methylpentene
View Answer
Explanation: In ‘z’ mechanism, the compounds with higher priority will be located opposite to each other of the double bond, in ‘E’ mechanism the compounds with high priority will be located in z corners and hence 3-methylpent-2-ene is the one which shows E-Z mechanism in which the priority group is CH3 and CH2CH3.
7. Which among the following is not colourless?
a) Methene
b) Ethene
c) Propene
d) Butene
View Answer
Explanation: Methene compound does not exist according to the formula CnH2n and also due to the lack of C=C.
8. Which among the following alkenes is used in the manufacturing of plastics?
a) Butadiene
b) 1,2-butadiene
c) 1,3-butadiene
d) 2-butadiene
View Answer
Explanation: Commonly this 1,3 butadiene is a widely used chemical in terms of a monomer as it has a very good electrical resistivity.
9. 4-chlorobut-1-ene is the name of which among the following alkenes?
a) CH2Cl-CH2=CH-CH2
b) CH2Cl-CH2-CH-CH2
c) CH2Cl=CH2-CH=CH2
d) CH2Cl-CH2-CH=CH2
View Answer
Explanation: The structure CH2Cl-CH2-CH=CH2 has the name 4Chlorobut-1-ene according to the IUPAC naming system.
10. Ethylene on reaction with bromine forms which among the following product?
a) BrH2C-CH2Br
b) BrH2C=CH2Br
c) Br2HC=CHBr2
d) Br2HC-CHBr2
View Answer
Explanation: The above reaction between Ethene and bromine is known as electrophilic halogenation reaction and the products usually formed are ethylene dihalides.
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