31. Which of the following is an example of optical isomerism?
A. 2-Butanol
B. But-2-ene
C. Propan-2-ol
D. 1-Butanol
Answer: A. 2-Butanol
Explanation:
Optical isomerism occurs when a molecule contains a chiral center, i.e., a carbon atom attached to four different groups. In 2-butanol, the second carbon is chiral, making it optically active.
32. Which one of the following reactions is an example of a Markovnikov addition?
A. Addition of HBr to propene
B. Addition of HBr to 1-butene in the presence of peroxide
C. Hydrogenation of ethyne
D. Oxidation of ethene with KMnO₄
Answer: A. Addition of HBr to propene
Explanation:
According to Markovnikov’s rule, in the addition of HX to an unsymmetrical alkene, the hydrogen atom bonds to the carbon with more hydrogen atoms (less substituted), and the halogen bonds to the more substituted carbon. This occurs in the addition of HBr to propene.
33. Which of the following compounds shows geometrical isomerism?
A. 1-Pentene
B. But-2-yne
C. 2-Methylpropene
D. But-2-ene
Answer: D. But-2-ene
Explanation:
Geometrical isomerism occurs due to restricted rotation around a double bond, and But-2-ene has cis and trans isomers based on the relative positions of the substituents around the double bond.
34. The major product in the dehydration of 2-methyl-2-butanol using concentrated H₂SO₄ is:
A. 2-Methyl-1-butene
B. 2-Methyl-2-butene
C. 3-Methyl-1-butene
D. 2-Butene
Answer: B. 2-Methyl-2-butene
Explanation:
Dehydration of alcohols in the presence of strong acids like H₂SO₄ proceeds via an E1 mechanism. According to Zaitsev’s rule, the more substituted alkene is the major product, which in this case is 2-Methyl-2-butene.
35. Which of the following undergoes nucleophilic substitution by an SN1 mechanism?
A. Methyl chloride
B. Ethyl chloride
C. Tert-butyl chloride
D. Propyl chloride
Answer: C. Tert-butyl chloride
Explanation:
Tertiary alkyl halides like tert-butyl chloride form stable carbocations and undergo nucleophilic substitution via the SN1 mechanism.
36. Which of the following pairs of compounds are chain isomers?
A. Propanol and Propanone
B. Butanal and 2-Methylpropanal
C. Butane and 2-Methylpropane
D. 2-Butene and 1-Butene
Answer: C. Butane and 2-Methylpropane
Explanation:
Chain isomers have the same molecular formula but differ in the arrangement of the carbon chain. Butane and 2-Methylpropane have the same molecular formula (C₄H₁₀) but different carbon chain structures.
37. Which of the following will undergo electrophilic aromatic substitution fastest?
A. Nitrobenzene
B. Benzene
C. Toluene
D. Chlorobenzene
Answer: C. Toluene
Explanation:
Toluene contains a methyl group, which is electron-donating and activates the benzene ring towards electrophilic substitution, making toluene more reactive than benzene and the other compounds.
38. Which of the following reactions is an example of an anti-Markovnikov addition?
A. Addition of HBr to propene in the presence of peroxide
B. Addition of HBr to propene
C. Nitration of benzene
D. Dehydration of alcohols
Answer: A. Addition of HBr to propene in the presence of peroxide
Explanation:
In the presence of peroxides, HBr adds to alkenes via the anti-Markovnikov rule (peroxide effect), where the bromine attaches to the less substituted carbon of the double bond.
39. The IUPAC name of the compound CH₃CH₂CH₂COOH is:
A. Propanoic acid
B. Butanoic acid
C. Pentanoic acid
D. 2-Butanoic acid
Answer: B. Butanoic acid
Explanation:
The compound contains a carboxylic acid group (-COOH) attached to a four-carbon chain, making the correct name butanoic acid.
40. Which of the following compounds shows both geometrical and optical isomerism?
A. 2-Butene
B. 2-Butanol
C. 3-Methylpent-2-ene
D. Butanal
Answer: C. 3-Methylpent-2-ene
Explanation:
3-Methylpent-2-ene exhibits geometrical isomerism due to the double bond and optical isomerism due to the presence of a chiral center at carbon 3.
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