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From amongst the following alcohols the one that would react fastest with conc. HCl and anhydrous ZnCI2, is:
- a)2 -Butanol
- b)2 -Methylpropan-2-ol
- c)2 -Methylpropanol
- d)1 -Butanol
Correct answer is option 'B'. Can you explain this answer?
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Most Upvoted Answer
From amongst the following alcohols the one that would react fastest w...
The alcohol that would react fastest with conc. HCl and anhydrous ZnCI2 is 2- methylpropan - 2- ol. It is a tertiary alcohol. A mixture of conc. HCl and anhydrous ZnCI2 is called Lucas reagent.
Primary alcohols react with Lucas reagent very slowly on heating to give alkyl chlorides. Secondary alcohols react with Lucas reagent much faster. Tertiary alcohols instantaneously react with HCl at room temperature.
Note: Lucas reagent is required for primary and secondary alcohol only.
Primary alcohols react with Lucas reagent very slowly on heating to give alkyl chlorides. Secondary alcohols react with Lucas reagent much faster. Tertiary alcohols instantaneously react with HCl at room temperature.
Note: Lucas reagent is required for primary and secondary alcohol only.
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From amongst the following alcohols the one that would react fastest w...
Understanding the Reaction
The reaction in question involves the conversion of alcohols to alkyl chlorides using concentrated HCl and anhydrous ZnCl2, often referred to as the Lucas test. The rate of this reaction depends on the structure of the alcohol.
Factors Influencing Reactivity
- Stability of Carbocation: The reaction proceeds via a carbocation intermediate. More stable carbocations lead to faster reactions.
- Degree of Substitution: Tertiary alcohols form more stable carbocations compared to secondary and primary alcohols.
Examining Each Alcohol
- 2-Butanol (Option A): This is a secondary alcohol. It forms a secondary carbocation, which is moderately stable.
- 2-Methylpropan-2-ol (Option B): This is a tertiary alcohol. Upon protonation, it forms a tertiary carbocation, which is highly stable due to hyperconjugation and inductive effects from surrounding alkyl groups. This makes it the fastest reacting alcohol among the options.
- 2-Methylpropanol (Option C): This is a primary alcohol. It forms a primary carbocation, which is the least stable and reacts the slowest.
- 1-Butanol (Option D): Like 2-Methylpropanol, this is also a primary alcohol and forms a primary carbocation.
Conclusion
Given that 2-Methylpropan-2-ol (Option B) forms a highly stable tertiary carbocation, it reacts the fastest with concentrated HCl and anhydrous ZnCl2 compared to the other alcohols listed. Thus, the correct answer is indeed option 'B'.
The reaction in question involves the conversion of alcohols to alkyl chlorides using concentrated HCl and anhydrous ZnCl2, often referred to as the Lucas test. The rate of this reaction depends on the structure of the alcohol.
Factors Influencing Reactivity
- Stability of Carbocation: The reaction proceeds via a carbocation intermediate. More stable carbocations lead to faster reactions.
- Degree of Substitution: Tertiary alcohols form more stable carbocations compared to secondary and primary alcohols.
Examining Each Alcohol
- 2-Butanol (Option A): This is a secondary alcohol. It forms a secondary carbocation, which is moderately stable.
- 2-Methylpropan-2-ol (Option B): This is a tertiary alcohol. Upon protonation, it forms a tertiary carbocation, which is highly stable due to hyperconjugation and inductive effects from surrounding alkyl groups. This makes it the fastest reacting alcohol among the options.
- 2-Methylpropanol (Option C): This is a primary alcohol. It forms a primary carbocation, which is the least stable and reacts the slowest.
- 1-Butanol (Option D): Like 2-Methylpropanol, this is also a primary alcohol and forms a primary carbocation.
Conclusion
Given that 2-Methylpropan-2-ol (Option B) forms a highly stable tertiary carbocation, it reacts the fastest with concentrated HCl and anhydrous ZnCl2 compared to the other alcohols listed. Thus, the correct answer is indeed option 'B'.
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From amongst the following alcohols the one that would react fastest with conc. HCl and anhydrous ZnCI2,is:a)2 -Butanolb)2 -Methylpropan-2-olc)2 -Methylpropanold)1 -ButanolCorrect answer is option 'B'. Can you explain this answer?
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