81. Which of the following undergoes nucleophilic substitution via the SN2 mechanism most easily?
A. Tert-butyl chloride
B. Isopropyl chloride
C. Ethyl chloride
D. Methyl chloride
Answer: D. Methyl chloride
Explanation:
The SN2 mechanism requires a backside attack by a nucleophile, which is easier when steric hindrance is minimal. Methyl chloride, having no bulky groups, undergoes SN2 substitution most easily.
82. Which of the following is a major product in the oxidation of 2-propanol?
A. Propanal
B. Acetone
C. Propanoic acid
D. Methane
Answer: B. Acetone
Explanation:
The oxidation of a secondary alcohol, such as 2-propanol, produces a ketone. In this case, acetone is formed as the major product.
83. Which of the following is an electrophile in the nitration of benzene?
A. H₂SO₄
B. NO₂⁺
C. HNO₃
D. SO₃
Answer: B. NO₂⁺
Explanation:
In the nitration of benzene, the nitronium ion (NO₂⁺) acts as the electrophile, attacking the electron-rich benzene ring to form nitrobenzene.
84. Which of the following reactions is an example of an elimination reaction?
A. Dehydration of ethanol to ethene
B. Hydrogenation of alkenes
C. Nitration of benzene
D. Hydrolysis of esters
Answer: A. Dehydration of ethanol to ethene
Explanation:
Elimination reactions involve the removal of atoms or groups from adjacent carbon atoms, forming a double bond. Dehydration of ethanol leads to the formation of ethene and water, making it an elimination reaction.
85. Which of the following is an optically active compound?
A. 2-Chlorobutane
B. 1-Chlorobutane
C. 2-Butene
D. Benzene
Answer: A. 2-Chlorobutane
Explanation:
Optical activity arises from chirality, where a compound has a carbon atom attached to four different groups. 2-Chlorobutane has such a chiral carbon, making it optically active.
86. Which of the following reagents is used for the oxidation of a primary alcohol to an aldehyde?
A. PCC (Pyridinium chlorochromate)
B. KMnO₄
C. H₂SO₄
D. NaBH₄
Answer: A. PCC (Pyridinium chlorochromate)
Explanation:
PCC is a selective oxidizing agent that oxidizes primary alcohols to aldehydes without further oxidation to carboxylic acids.
87. Which of the following undergoes nucleophilic addition reactions most readily?
A. Benzene
B. Ethene
C. Formaldehyde
D. Methane
Answer: C. Formaldehyde
Explanation:
Aldehydes, especially formaldehyde, undergo nucleophilic addition reactions readily due to the partial positive charge on the carbonyl carbon, making it susceptible to attack by nucleophiles.
88. Which of the following exhibits cis-trans isomerism?
A. 2-Butene
B. Propane
C. 2-Propanol
D. 1-Chloropropane
Answer: A. 2-Butene
Explanation:
Cis-trans (geometrical) isomerism occurs in alkenes with restricted rotation around a double bond. 2-Butene has both cis and trans forms due to the arrangement of groups around the double bond.
89. Which of the following is the correct IUPAC name for CH₃CH₂COCH₃?
A. Propanone
B. Butanone
C. 2-Propanol
D. 3-Butanol
Answer: B. Butanone
Explanation:
The compound is a four-carbon ketone where the carbonyl group is located on the second carbon. The correct IUPAC name is butanone.
90. Which of the following compounds undergoes free radical halogenation most easily?
A. Methane
B. Ethane
C. Propane
D. Isobutane
Answer: D. Isobutane
Explanation:
Free radical halogenation proceeds more readily with alkanes that can form stable radicals. Isobutane forms a tertiary radical, which is more stable than the radicals formed by methane, ethane, or propane.
91. Which of the following reactions is an example of a reduction reaction?
A. Hydrogenation of ethene to ethane
B. Dehydration of ethanol to ethene
C. Oxidation of ethanol to acetic acid
D. Hydrolysis of esters
Answer: A. Hydrogenation of ethene to ethane
Explanation:
Reduction reactions involve the gain of electrons or hydrogen atoms. In the hydrogenation of ethene, hydrogen is added to the double bond, reducing it to ethane.
92. Which of the following is the major product of the reaction of but-1-ene with HCl?
A. 1-Chlorobutane
B. 2-Chlorobutane
C. Butanol
D. 1,2-Dichlorobutane
Answer: B. 2-Chlorobutane
Explanation:
According to Markovnikov’s rule, the hydrogen atom adds to the carbon with more hydrogen atoms, and the chlorine adds to the more substituted carbon, forming 2-chlorobutane.
93. Which of the following compounds shows optical isomerism?
A. 2-Bromobutane
B. 1-Bromobutane
C. 2-Butene
D. Cyclohexane
Answer: A. 2-Bromobutane
Explanation:
Optical isomerism occurs when a molecule has a chiral center. 2-Bromobutane has a chiral carbon atom attached to four different groups, leading to optical isomerism
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