This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Enamines”.
1. What is the name of the given compound?
a) Amine
b) Imine
c) Enamine
d) Amide
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Explanation: An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Enamines are versatile intermediates.
2. The phenomenon or process by which imine are converted into enamine is which of the following?
a) Imination
b) Enamination
c) Amination
d) Tautomerism
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Explanation: The enamine-imine tautomerism may be considered analogous to the keto-enol tautomerism. In both cases, a hydrogen atom switches its location between the heteroatom (oxygen or nitrogen) and the second carbon atom.
3. Which of the following is not true about enamines?
a) Enamine are derived by the condensation of an aldehyde or ketone with a primary amine
b) Enamines are versatile intermediates
c) Enamines are considered to be nitrogen analogs of enols
d) They are tautomeric form of imine
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Explanation: An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Primary amines are usually not used for enamine synthesis due to the preferential formation of the more thermodynamically stable imine species.
4. Enamine shows which type of behavior?
a) Basic
b) Electrophilic and acidic
c) Nucleophilic and basic
d) Nucleophilic
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Explanation: Enamines are both good nucleophiles and good bases. Their behaviour as carbon-based nucleophiles are explained with reference to the following resonance structures.
5. What is the type of the following reaction?
a) Condensation reaction
b) Acylation reaction
c) Rearrangement reaction
d) Redox reaction
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Explanation: An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine.
6. What is the name of the compound A in the given reaction of formation of enamine?
a) Imine
b) Amine
c) Carbinoamine
d) Amide
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Explanation: Methyl ketone self-condensation is a side-reaction which can be avoided through the addition of TiCl4 into the reaction mixture (to act as a water scavenger). This is an example of an aldehyde reacting with a secondary amine to form an enamine via a carbinolamine intermediate.
7. What is the name of the compound A in the given reaction of enamine?
a) Imine salt
b) Amine
c) Carbinoamine
d) Amide
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Explanation: The enamine nucleophile can attack haloalkanes to form the alkylated iminium salt intermediate which then hydrolyzes to regenerate a ketone (a starting material in enamine synthesis).
8. What is the name of the compound formed when alkylation of enamine is followed by hydrolysis?
a) Carboxylic acid
b) Ketone
c) Amide
d) ester
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Explanation: The enamine nucleophile can attack haloalkanes to form the alkylated iminium salt intermediate which then hydrolyzes to regenerate a ketone.
9. What is the name of the following reaction of enamine?
a) Condensation reaction
b) Alkylation reaction
c) Rearrangement reaction
d) Redox reaction
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Explanation: This reaction is an alkylation reaction, in which, the enamine nucleophile can attack haloalkanes to form the alkylated iminium salt intermediate which then hydrolyzes to regenerate a ketone. This reaction was pioneered by Gilbert Stork, and is sometimes referred to by the name of its inventor.
10. Which cyclic ketone enamine is most reactive?
a) Five membered
b) Six membered
c) Seven membered
d) Eight membered
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Explanation: Cyclic ketone enamines follow a reactivity trend where the five membered ring is the most reactive due to its maximally planar conformation at the nitrogen.
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