NEET Chemistry: Identification of primary secondary and tertiary alcohols and dehydration mechanism Practice Questions
14 free multiple-choice questions on Identification of primary secondary and tertiary alcohols and dehydration mechanism (Alcohols, Phenols, and Ethers) for NEET Chemistry, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.
Practice thousands more NEET questions in the app →Q1. Which structural feature generally dictates the ease with which an alcohol can be converted into an alkene during dehydration?
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Correct answer: C — The substitution pattern (1°, 2°, 3° alcohol)
The substitution pattern (primary, secondary, or tertiary) dictates the stability of the intermediate carbocation formed during the elimination process, which in turn affects the ease of the reaction.
Q2. Identify the degree of unsaturation in 2-methyl-2-butanol (an alcohol).
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Correct answer: C — 0
2-methyl-2-butanol is a saturated alcohol, meaning it contains only single bonds between carbon atoms. Therefore, its degree of unsaturation is 0.
Q3. Which of the following statements correctly describes the major product formed upon the acid-catalyzed dehydration of a tertiary alcohol?
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Correct answer: D — The reaction involves carbocation intermediate, which may undergo rearrangement to form a more stable carbocation, leading to a different alkene product.
Tertiary alcohols undergo dehydration via an E1 mechanism, involving the formation of a stable tertiary carbocation. Since the reaction proceeds through a carbocation intermediate, rearrangement (hydride shift) is possible if a more stable carbocation can be formed. This process often leads to the formation of multiple possible alkene isomers, making rearrangement a crucial consideration in predicting the final product distribution.
Q4. Which functional group among the following is directly involved in the typical dehydration process of alcohols?
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Correct answer: C — Alcohol OH group
The dehydration reaction specifically involves the removal of water from the hydroxyl (OH) group of the alcohol to form an unsaturated hydrocarbon (alkene).
Q5. In the acid-catalyzed dehydration of 2-butanol, the major alkene product formed is:
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Correct answer: D — 2-Butene
Following Zaitsev's rule, the major product results from the more substituted (more stable) alkene. Dehydration of 2-butanol yields 2-butene (a mixture of cis/trans isomers), which is the most substituted product.
Q6. Which of the following is an example of a secondary alcohol?
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Correct answer: C — 2-Propanol
2-Propanol has the hydroxyl group attached to a carbon that is bonded to two other carbon atoms, classifying it as a secondary alcohol.
Q7. Which type of alcohol generally undergoes acid-catalyzed dehydration to form alkenes via an E1 mechanism?
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Correct answer: D — Tertiary alcohols
Tertiary alcohols form stable tertiary carbocations during the mechanism, making them highly prone to undergoing elimination reactions (dehydration).
Q8. Which reaction pathway is generally favored during the dehydration of secondary alcohols over tertiary alcohols?
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Correct answer: C — E1
Dehydration often proceeds via the E1 mechanism, which is highly dependent on the stability of the intermediate carbocation. For secondary alcohols, the intermediate is secondary, allowing E1 elimination.
Q9. For an alcohol structure, the stability of the resulting carbocation intermediate formed during dehydration follows which order?
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Correct answer: C — Tertiary > Secondary > Primary
The stability of carbocations derived from the dehydration pathway follows the order: Tertiary (R₃C⁺) > Secondary (R₂C⁺) > Primary (RCH₂⁺).
Q10. When a tertiary alcohol undergoes acid-catalyzed dehydration, what is the major type of elimination reaction that occurs?
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Correct answer: C — E1
Tertiary alcohols readily form stable tertiary carbocations, which facilitates the subsequent elimination step, leading primarily to the E1 reaction.
Q11. The dehydration of a primary alcohol typically proceeds via which mechanism?
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Correct answer: D — E1 mechanism
Dehydration of primary alcohols usually involves the formation of a primary carbocation intermediate, thus favoring the unimolecular elimination mechanism (E1).
Q12. Which statement accurately describes the general trend in reactivity for alcohols towards acid-catalyzed reactions?
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Correct answer: A — Secondary alcohols are most reactive
Secondary alcohols typically exhibit the highest reactivity towards electrophilic reactions (like dehydration) compared to primary alcohols because the resulting intermediate stability is optimized in this case.
Q13. Identify the type of alcohol present in the molecule CH₃CH(OH)CH₃ (Propan-2-ol).
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Correct answer: C — Secondary alcohol
In Propan-2-ol, the carbon atom bonded to the OH group is bonded to two other carbon atoms. Therefore, it is classified as a secondary alcohol.
Q14. The elimination reaction involving alcohols often proceeds via a mechanism that involves a highly unstable intermediate. Which type of alcohol is most likely to undergo this pathway easily?
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Correct answer: C — Tertiary alcohols
Tertiary alcohols facilitate the elimination reaction efficiently because the formation of a stable tertiary carbocation is achievable, which drives the elimination step.
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