Reaction Mechanisms: Substitution, Addition, Elimination
Q. In an addition reaction involving alkenes, what is the product when HBr is added to propene?
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A.
1-bromopropane
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B.
2-bromopropane
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C.
Propyl bromide
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D.
Bromopropane
Solution
The addition of HBr to propene follows Markovnikov's rule, leading to the formation of 1-bromopropane.
Correct Answer: B — 2-bromopropane
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Q. In an E2 elimination reaction, what is the role of the base?
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A.
To donate a proton
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B.
To stabilize the carbocation
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C.
To act as a leaving group
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D.
To form a cyclic intermediate
Solution
In an E2 reaction, the base abstracts a proton from the β-carbon, facilitating the elimination of the leaving group and formation of a double bond.
Correct Answer: A — To donate a proton
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Q. In an SN2 reaction, what is the stereochemical outcome when the nucleophile attacks a chiral center?
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A.
Retention of configuration
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B.
Inversion of configuration
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C.
No change in configuration
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D.
Formation of a racemic mixture
Solution
In an SN2 reaction, the nucleophile attacks from the opposite side of the leaving group, resulting in inversion of configuration.
Correct Answer: B — Inversion of configuration
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Q. What is the IUPAC name for the compound CH3-CH2-CH(CH3)-CH2-Br?
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A.
1-bromo-3-methylbutane
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B.
2-bromo-3-methylbutane
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C.
3-bromo-2-methylbutane
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D.
1-bromo-2-methylbutane
Solution
The longest carbon chain has four carbons, and the bromine is on the first carbon when numbering from the end closest to the substituent.
Correct Answer: A — 1-bromo-3-methylbutane
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Q. What is the IUPAC name for the compound with the structure CH3-CH(CH3)-C(=O)-OH?
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A.
3-methylbutanoic acid
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B.
2-methylbutanoic acid
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C.
3-methylbutanal
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D.
2-methylbutanal
Solution
The compound is a carboxylic acid with a four-carbon chain and a methyl group on the second carbon, hence 2-methylbutanoic acid.
Correct Answer: B — 2-methylbutanoic acid
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Q. What is the major product of the elimination reaction of 2-bromobutane with a strong base?
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A.
Butene
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B.
2-butene
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C.
1-butene
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D.
Butyne
Solution
The major product of the elimination of 2-bromobutane with a strong base is butene, specifically 2-butene due to the more stable alkene formation.
Correct Answer: B — 2-butene
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Q. What is the major product of the reaction between 1-butene and H2 in the presence of a catalyst?
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A.
1-butene
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B.
2-butene
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C.
Butane
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D.
Cyclobutane
Solution
The hydrogenation of 1-butene leads to the formation of butane as the major product.
Correct Answer: C — Butane
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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)?
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A.
Nucleophile attacks from the back side, leading to inversion of configuration
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B.
Nucleophile attacks from the front side, leading to retention of configuration
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C.
Formation of a carbocation intermediate
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D.
Nucleophile attacks the halogen first
Solution
In an SN2 reaction, the nucleophile attacks the carbon from the opposite side of the leaving group, resulting in inversion of configuration.
Correct Answer: A — Nucleophile attacks from the back side, leading to inversion of configuration
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Q. What is the stereochemical configuration of the product formed from the reaction of (R)-2-bromobutane with a strong nucleophile in an SN2 reaction?
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A.
R
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B.
S
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C.
R and S
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D.
Neither R nor S
Solution
The SN2 reaction will invert the configuration of (R)-2-bromobutane, resulting in the (S) configuration.
Correct Answer: B — S
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Q. What type of reaction mechanism is involved when a nucleophile replaces a leaving group in an alkyl halide?
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A.
Elimination
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B.
Substitution
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C.
Addition
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D.
Rearrangement
Solution
This is a substitution reaction mechanism, where a nucleophile replaces a leaving group.
Correct Answer: B — Substitution
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Q. What type of stereochemistry is observed in an SN2 reaction?
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A.
Racemic mixture
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B.
Retention of configuration
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C.
Inversion of configuration
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D.
No stereochemistry change
Solution
SN2 reactions result in inversion of configuration due to the backside attack of the nucleophile.
Correct Answer: C — Inversion of configuration
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Q. Which functional group is formed in the addition reaction of an alkene with HBr?
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A.
Alcohol
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B.
Alkane
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C.
Alkyl halide
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D.
Ether
Solution
The addition of HBr to an alkene results in the formation of an alkyl halide.
Correct Answer: C — Alkyl halide
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Q. Which of the following compounds can undergo an E1 elimination reaction?
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A.
1-bromobutane
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B.
2-bromobutane
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C.
3-bromobutane
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D.
Cyclohexyl bromide
Solution
2-bromobutane can undergo E1 elimination due to the stability of the carbocation formed during the reaction.
Correct Answer: B — 2-bromobutane
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Q. Which of the following compounds undergoes an SN1 reaction most readily?
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A.
1-bromopropane
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B.
2-bromopropane
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C.
3-bromopropane
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D.
1-bromo-2-methylpropane
Solution
Tertiary alkyl halides like 3-bromopropane stabilize the carbocation intermediate formed during the SN1 mechanism, making them more reactive.
Correct Answer: C — 3-bromopropane
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Q. Which of the following is a characteristic of an E2 elimination reaction?
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A.
It involves a carbocation intermediate
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B.
It requires a strong base
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C.
It occurs in a single step
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D.
Both B and C
Solution
E2 reactions require a strong base and occur in a single step, eliminating a leaving group and a hydrogen atom.
Correct Answer: D — Both B and C
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Q. Which of the following is a characteristic of an elimination reaction?
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A.
Formation of a double bond
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B.
Formation of a single bond
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C.
Addition of a nucleophile
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D.
Formation of a carbocation
Solution
Elimination reactions typically involve the removal of atoms or groups from a molecule, resulting in the formation of a double bond.
Correct Answer: A — Formation of a double bond
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Q. Which of the following statements is true regarding the E1 mechanism?
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A.
It involves a concerted mechanism
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B.
It forms a carbocation intermediate
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C.
It requires a strong base
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D.
It is stereospecific
Solution
E1 reactions involve the formation of a carbocation intermediate, followed by deprotonation to form the alkene.
Correct Answer: B — It forms a carbocation intermediate
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Q. Which of the following statements is true regarding the mechanism of an SN1 reaction?
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A.
It involves a concerted mechanism
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B.
It has a carbocation intermediate
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C.
It is stereospecific
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D.
It requires a strong nucleophile
Solution
SN1 reactions involve the formation of a carbocation intermediate, making them unimolecular.
Correct Answer: B — It has a carbocation intermediate
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