The Question is from neet-chemistry hydrocarbons alkynes, and it was created by the author Mr. S M HUSSAIN

Question

Which of the following alkynes upon reaction with $HgSO_4$ and $H_2SO_4$ yields a product that exhibits keto-enol tautomerism?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
	**Primary Concept**: Hydration of Alkynes
	**Related Topics**: Markovnikov's Rule, Keto-Enol Tautomerism, Alkynes, Organic Chemistry
	**Prerequisites**: Understanding of alkyne reactions and tautomerism.
## SOLUTION PATHWAY
**Given Information**:
	Reaction of alkynes with $HgSO_4$ and $H_2SO_4$ (acid-catalyzed hydration).
	Need to identify the alkyne that yields a product capable of keto-enol tautomerism.
**Method & Steps**:
	1. Recall the mechanism of acid-catalyzed hydration of alkynes.
		Reasoning: This reaction follows Markovnikov's rule, adding water across the triple bond.
		Formula/Rule: Alkynes react with $HgSO_4$ and $H_2SO_4$ to form ketones (except for terminal alkynes which can form both ketones and aldehydes).
	2. Analyze the given alkynes and their potential products.
		Working:  Consider the products formed by each alkyne:
			- 1-butyne forms a methyl ketone.
			- 2-butyne forms a ketone with no alpha hydrogens.
			- 3-hexyne forms a ketone with no alpha hydrogens.
			- 2,2-dimethyl-3-hexyne forms a ketone with no alpha hydrogens.
		Key Point: Keto-enol tautomerism requires an alpha hydrogen next to the carbonyl group.
	3. Identify the alkyne that produces a ketone with alpha hydrogens.
		Result: Only 1-butyne forms a methyl ketone (2-butanone) which has alpha hydrogens and thus exhibits keto-enol tautomerism.
		Verification: The other options form ketones that lack alpha hydrogens and cannot undergo tautomerism.
## OPTION ANALYSIS
[A] :x: 2-butyne forms 2-butanone, which has no alpha hydrogens. Thus, keto-enol tautomerism is not possible.
[B] ✓: 1-butyne forms 2-butanone (a methyl ketone) which has alpha hydrogens.  Thus, it exhibits keto-enol tautomerism.
[C] :x: 3-hexyne forms 3-hexanone, which has no alpha hydrogens.  Thus, keto-enol tautomerism is not possible.
[D] :x: 2,2-dimethyl-3-hexyne forms 2,2-dimethyl-3-hexanone, which has no alpha hydrogens.  Thus, keto-enol tautomerism is not possible.
## LEARNING AIDS
	**Common Mistakes**:
		1. Forgetting Markovnikov's rule: Remember that the more substituted carbon gets the hydroxyl group during hydration.
		2. Not recognizing the requirement of alpha hydrogens for keto-enol tautomerism:  Ensure the product has a hydrogen atom on the carbon adjacent to the carbonyl group.
	**Quick Tips**:
		1. Terminal alkynes upon hydration with $HgSO_4$/$H_2SO_4$ typically yield methyl ketones which can exhibit keto-enol tautomerism.
		2. Look for alpha hydrogens in the product ketone to determine if tautomerism is possible.

Mr. S M HUSSAIN · Answer

2-butyne

Mr. S M HUSSAIN · Answer

The correct Option is "1-butyne"

Mr. S M HUSSAIN · Answer

3-hexyne

Mr. S M HUSSAIN · Answer

2,2-dimethyl-3-hexyne

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