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

Question

Which of the following reactions involving propyne would NOT produce a ketone as the major product?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Electrophilic addition and reduction reactions of alkynes.
 **Related Topics**: Markovnikov's rule, tautomerism, enol-keto tautomerism.
 **Prerequisites**: Understanding of alkyne reactivity, mechanisms of hydration, hydroboration-oxidation, and reduction with sodium in liquid ammonia.
## SOLUTION PATHWAY
**Given Information**:
  Propyne ($CH_3C≡CH$) is the reactant.
  Four different reactions are given as options.
**Method & Steps**:
 1. Analyze each reaction to determine the major product.
  Reasoning: We need to examine which reaction doesn't yield a ketone as the primary product.
 2. Identify the reaction that doesn't lead to a ketone.
  Working:
  A. Reaction with $HgSO_4$ and $H_2SO_4$: This is the acid-catalyzed hydration of an alkyne.  It follows Markovnikov's rule, leading to the formation of a ketone (propan-2-one).
  B. Reaction with $BH_3$ followed by $H_2O_2$ in alkaline medium: This is hydroboration-oxidation.  It follows anti-Markovnikov addition, forming an enol which tautomerizes to a ketone (propanal).
  C. Reaction with $Na$ in liquid $NH_3$: This is a reduction reaction. Sodium in liquid ammonia reduces alkynes to trans alkenes.  No ketone is formed. Propyne is reduced to propene.
  D. Reaction with $Hg(OAc)_2$ followed by $NaBH_4$: This is oxymercuration-demercuration. It's similar to the acid-catalyzed hydration (option A) and also yields a ketone (propan-2-one).
 3. Determine the final answer.
  Result: Option C is the correct answer because it does not produce a ketone.  It produces an alkene instead.
  Verification: The mechanisms of each reaction confirm the products.
 ## OPTION ANALYSIS
A ✓: Acid-catalyzed hydration produces a ketone via an enol intermediate.
B :x: Hydroboration-oxidation produces an aldehyde which is not a ketone, but this is converted to a ketone (propanal) via tautomerization.
 C :x: Reduction with sodium in liquid ammonia gives a trans alkene, not a ketone.
D :x: Oxymercuration-demercuration yields a ketone.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing Markovnikov's and anti-Markovnikov's addition: Remember that Markovnikov's rule applies to electrophilic addition, while anti-Markovnikov's rule applies to hydroboration-oxidation.
  2. Forgetting enol-keto tautomerism: Enols readily tautomerize to ketones or aldehydes.
 **Quick Tips**:
  1.Memorize the common reactions of alkynes and their products.
  2.Draw the reaction mechanisms to visualize the steps and products.

Mr. S M HUSSAIN · Answer

Reaction with $HgSO_4$ and $H_2SO_4$

Mr. S M HUSSAIN · Answer

Reaction with $BH_3$ followed by $H_2O_2$ in alkaline medium

Mr. S M HUSSAIN · Answer

The correct Option is "Reaction with $Na$ in liquid $NH_3$"

Mr. S M HUSSAIN · Answer

Reaction with $Hg(OAc)_2$ followed by $NaBH_4$

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