The Question is from neet-chemistry alcohols-phenols-ethers , and it was created by the author P SRAVAN KUMAR

Question

An unknown alcohol reacts with Lucas reagent to give turbidity within 5 minutes.  Upon oxidation with Jones reagent, it yields a ketone. The alcohol could be:

P SRAVAN KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Lucas test and Jones oxidation of alcohols
 **Related Topics**:  Reactions of alcohols, identification of alcohols, oxidation states
 **Prerequisites**: Understanding of the Lucas test (reaction of alcohols with $	ext{ZnCl}_2$ and HCl), Jones oxidation (oxidation of alcohols using chromic acid), and the structures of alcohols and ketones.
## SOLUTION PATHWAY
**Given Information**:
  * The alcohol reacts with Lucas reagent to give turbidity within 5 minutes.
  * Oxidation with Jones reagent yields a ketone.
**Method & Steps**:
 1. **Lucas Test:** The Lucas test differentiates between primary, secondary, and tertiary alcohols based on the rate of reaction with Lucas reagent ($	ext{ZnCl}_2$ in concentrated HCl). Tertiary alcohols react immediately, secondary alcohols react within 5-10 minutes, and primary alcohols react slowly or not at all.
  Reasoning: Since turbidity appears within 5 minutes, the alcohol is either secondary or tertiary.
  Formula/Rule:  No specific formula, but the reaction mechanism involves the formation of a carbocation.
 2. **Jones Oxidation:** Jones oxidation ($CrO_3$ in aqueous sulfuric acid) oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones. Primary alcohols do not yield ketones upon oxidation.
  Working: The fact that oxidation yields a ketone indicates that the alcohol is secondary.
  Key Point: The combination of a relatively fast Lucas test and ketone formation upon oxidation uniquely points to a secondary alcohol.
 3. **Identification:** We need a secondary alcohol that would react with Lucas reagent within 5 minutes.
  Result: 2-pentanol is a secondary alcohol that would fit this description.  The other options either react too slowly (primary alcohols) or react too quickly (tertiary alcohols) with Lucas reagent, or don't yield a ketone upon Jones oxidation.
  Verification: 2-pentanol is a secondary alcohol, and its reaction with Lucas reagent is consistent with a reaction time of 5 minutes.  Jones oxidation will convert it into a ketone (2-pentanone).
 ## OPTION ANALYSIS
A :x: 1-pentanol is a primary alcohol; it would react very slowly or not at all with Lucas reagent and would yield a carboxylic acid upon Jones oxidation, not a ketone.
B :x: 2-methyl-2-butanol is a tertiary alcohol; it would react immediately with Lucas reagent.
 C ✓: 2-pentanol is a secondary alcohol; it would react within 5-10 minutes with Lucas reagent and yield a ketone (2-pentanone) upon Jones oxidation.
D :x: 2,2-dimethyl-1-propanol is a primary alcohol; it would react slowly or not at all with Lucas reagent and would yield a carboxylic acid upon Jones oxidation, not a ketone.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the reactivity of primary, secondary, and tertiary alcohols in the Lucas test: Remember the order of reactivity: tertiary > secondary > primary.
  2.Misinterpreting the products of Jones oxidation:  Know that primary alcohols yield carboxylic acids and secondary alcohols yield ketones.
 **Quick Tips**:
  1.Use a flowchart to summarize the information from the Lucas test and Jones oxidation to easily identify the type of alcohol.
  2.Memorize the reactivity trends of alcohols with different reagents.

P SRAVAN KUMAR · Answer

1-pentanol

P SRAVAN KUMAR · Answer

2-methyl-2-butanol

P SRAVAN KUMAR · Answer

The correct Option is "2-pentanol"

P SRAVAN KUMAR · Answer

2,2-dimethyl-1-propanol

NEET Chemistry Alcohols, Phenols And Ethers MCQs

Select Topic

Question Tags

NEET Subjects

Our Bots

Company