1. Which of the following is the correct IUPAC name for the compound CH₃-CH₂-CH₂-CH(OH)-CH₃?
A. 3-Hydroxy-2-pentanol
B. 2-Pentanol
C. 3-Pentanol
D. Pentan-2-ol
Answer: D. Pentan-2-ol
Explanation:
The longest carbon chain contains 5 carbon atoms, hence the base name is pentane. The -OH group is attached to the second carbon, so the compound is named as pentan-2-ol according to IUPAC rules.
2. Which of the following represents a pair of functional isomers?
A. C₂H₅OH and CH₃OCH₃
B. C₆H₆ and C₆H₁₂
C. C₂H₆O and CH₃COOH
D. CH₃CH₂CH₂OH and CH₃CH₂CH₂CH₃
Answer: A. C₂H₅OH and CH₃OCH₃
Explanation:
Functional isomers have the same molecular formula but different functional groups. C₂H₅OH is ethanol (alcohol) and CH₃OCH₃ is dimethyl ether (ether). Both have the same molecular formula (C₂H₆O) but different functional groups (alcohol and ether).
3. Which of the following represents geometrical isomerism?
A. But-2-ene
B. 1-Butene
C. Propene
D. 2-Methylpropene
Answer: A. But-2-ene
Explanation:
Geometrical isomerism occurs due to the restricted rotation around a double bond and the presence of different groups attached to the double-bonded carbons. In but-2-ene, there is a possibility of cis and trans isomers because of the presence of two different groups on each carbon of the double bond.
4. Which of the following reactions follows the SN1 mechanism?
A. CH₃Cl + OH⁻
B. (CH₃)₃CCl + OH⁻
C. CH₃CH₂Cl + OH⁻
D. C₆H₅CH₂Cl + OH⁻
Answer: B. (CH₃)₃CCl + OH⁻
Explanation:
SN1 mechanism involves a two-step process where the rate-determining step is the formation of a carbocation. Tertiary alkyl halides like (CH₃)₃CCl form stable carbocations and hence undergo substitution via the SN1 mechanism.
5. Which one of the following pairs can exhibit tautomerism?
A. Acetone and Propanol
B. Ethanol and Methanal
C. Acetaldehyde and Acetic acid
D. Acetone and Acetaldehyde
Answer: D. Acetone and Acetaldehyde
Explanation:
Tautomerism is a phenomenon where compounds exist in equilibrium between two structural forms, usually keto and enol forms. Both acetone (a ketone) and acetaldehyde (an aldehyde) can show keto-enol tautomerism.
6. Which of the following reactions involves an electrophilic substitution mechanism?
A. Halogenation of alkanes
B. Nitration of benzene
C. Hydrolysis of esters
D. Dehydration of alcohols
Answer: B. Nitration of benzene
Explanation:
Electrophilic substitution reactions typically occur in aromatic compounds like benzene. In the nitration of benzene, a nitronium ion (NO₂⁺) acts as the electrophile and substitutes a hydrogen atom in the benzene ring.
7. Which of the following compounds exhibits optical isomerism?
A. 2-Butanol
B. Propan-2-ol
C. 1-Butanol
D. 2-Methylpropane
Answer: A. 2-Butanol
Explanation:
Optical isomerism arises when a compound contains a chiral center, i.e., a carbon atom bonded to four different groups. In 2-butanol, the second carbon is attached to four different groups, making it optically active.
8. In the reaction mechanism of nucleophilic substitution, the rate of reaction for SN2 depends on:
A. Concentration of the nucleophile only
B. Concentration of alkyl halide only
C. Both nucleophile and alkyl halide concentrations
D. None of the above
Answer: C. Both nucleophile and alkyl halide concentrations
Explanation:
In the SN2 mechanism, the reaction occurs in a single step where the nucleophile attacks the substrate, leading to the simultaneous breaking of the carbon-halogen bond. The rate of reaction depends on both the nucleophile and the substrate concentrations.
9. Which of the following 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. Hydration 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 (where X is a halogen) to an alkene, the hydrogen atom attaches to the carbon with the greater number of hydrogen atoms (the less substituted carbon), while the halogen attaches to the more substituted carbon. This is seen in the addition of HBr to propene.
10. Which of the following is an anti-Markovnikov addition reaction?
A. Addition of HBr to 1-butene in the presence of peroxide
B. Addition of H₂O to ethene
C. Nitration of benzene
D. Sulphonation of benzene
Answer: A. Addition of HBr to 1-butene in the presence of peroxide
Explanation:
The presence of peroxides leads to an anti-Markovnikov addition of HBr, where the bromine attaches to the less substituted carbon. This reaction is also known as the peroxide effect or Kharasch effect.
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