Reaction Mechanisms: Substitution, Addition, Elimination - Competitive Exam Level
Q. In an addition reaction of HBr to an alkene, what is the major product when the alkene is asymmetric?
A.
The product with the bromine on the more substituted carbon.
B.
The product with the bromine on the less substituted carbon.
C.
A racemic mixture of products.
D.
No reaction occurs.
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Solution
According to Markovnikov's rule, in the addition of HBr to an asymmetric alkene, the hydrogen will add to the less substituted carbon, and the bromine will add to the more substituted carbon.
Correct Answer: A — The product with the bromine on the more substituted carbon.
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Q. In an SN1 reaction, which step is rate-determining?
A.
Formation of the carbocation
B.
Nucleophilic attack
C.
Deprotonation
D.
Rearrangement
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Solution
The formation of the carbocation is the rate-determining step in an SN1 reaction, as it involves breaking the bond to the leaving group.
Correct Answer: A — Formation of the carbocation
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Q. What is the IUPAC name of the compound CH3-CH2-CH(CH3)-CH2-Br?
A.
1-bromobutane
B.
2-bromobutane
C.
3-bromobutane
D.
1-bromo-2-methylpropane
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Solution
The longest carbon chain has four carbons, and the bromine is attached to the second carbon, making the IUPAC name 2-bromobutane.
Correct Answer: B — 2-bromobutane
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Q. What is the major product of the reaction of 2-methylpropene with HBr?
A.
2-bromopropane
B.
1-bromopropane
C.
3-bromopropane
D.
2-bromo-2-methylpropane
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Solution
The major product is 2-bromopropane due to Markovnikov's rule, where the bromine adds to the more substituted carbon.
Correct Answer: A — 2-bromopropane
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Q. What is the mechanism of the reaction between 1-bromobutane and sodium hydroxide in ethanol?
A.
SN1
B.
SN2
C.
E1
D.
E2
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Solution
The reaction proceeds via an SN2 mechanism due to the primary nature of 1-bromobutane, allowing for a backside attack by the nucleophile.
Correct Answer: B — SN2
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Q. What is the mechanism of the reaction between an alkyl halide and a nucleophile in a bimolecular nucleophilic substitution (SN2) reaction?
A.
The nucleophile attacks the carbon from the opposite side of the leaving group.
B.
The nucleophile attacks the carbon from the same side as the leaving group.
C.
The reaction proceeds through a carbocation intermediate.
D.
The reaction involves the formation of a cyclic intermediate.
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Solution
In an SN2 reaction, the nucleophile attacks the carbon atom from the opposite side of the leaving group, leading to a backside attack and inversion of configuration.
Correct Answer: A — The nucleophile attacks the carbon from the opposite side of the leaving group.
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Q. What is the product of the reaction between benzyl chloride and sodium hydroxide in water?
A.
Benzyl alcohol
B.
Benzyl ether
C.
Benzyl amine
D.
Benzyl bromide
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Solution
The reaction proceeds via an SN2 mechanism, resulting in the formation of benzyl alcohol.
Correct Answer: A — Benzyl alcohol
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Q. Which functional group is present in the compound CH3-COOH?
A.
Alcohol
B.
Aldehyde
C.
Carboxylic acid
D.
Ester
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Solution
The compound CH3-COOH contains a carboxylic acid functional group, characterized by the -COOH group.
Correct Answer: C — Carboxylic acid
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Q. Which of the following is a characteristic of a nucleophile?
A.
It donates electrons.
B.
It accepts electrons.
C.
It is always neutral.
D.
It is always positively charged.
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Solution
A nucleophile is characterized by its ability to donate electrons to form a bond with an electrophile.
Correct Answer: A — It donates electrons.
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Q. Which of the following is a characteristic of an E1 mechanism?
A.
It involves a concerted mechanism.
B.
It requires a strong base.
C.
It forms a carbocation intermediate.
D.
It occurs only with primary substrates.
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Solution
E1 mechanisms involve the formation of a carbocation intermediate, which is a key feature of this type of elimination reaction.
Correct Answer: C — It forms a carbocation intermediate.
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Q. Which of the following statements is true regarding nucleophiles?
A.
They are electron-deficient species.
B.
They donate electrons to electrophiles.
C.
They are always negatively charged.
D.
They cannot be neutral molecules.
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Solution
Nucleophiles are electron-rich species that donate electrons to electrophiles during chemical reactions.
Correct Answer: B — They donate electrons to electrophiles.
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Q. Which of the following statements is true regarding the E1 elimination mechanism?
A.
It involves a concerted mechanism.
B.
It proceeds through a carbocation intermediate.
C.
It is favored by strong bases.
D.
It results in stereospecific products.
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Solution
E1 elimination proceeds through a carbocation intermediate, making it a two-step process.
Correct Answer: B — It proceeds through a carbocation intermediate.
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