The Question is from neet-chemistry hydrocarbons , and it was created by the author THIRUPATHI REDDY

Question

The reaction of 1 equivalent of $HBr$ with 1-phenylpropyne in the presence of peroxides yields predominantly:

THIRUPATHI REDDY · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Free radical addition of HBr to alkynes
 **Related Topics**: Markovnikov's rule, anti-Markovnikov addition, peroxide effect
 **Prerequisites**: Understanding of free radical mechanisms, alkyne structure
## SOLUTION PATHWAY
**Given Information**:
  1 equivalent of $HBr$
  1-phenylpropyne ($C_6H_5C≡CCH_3$)
  Presence of peroxides
  [Important conditions]: Peroxides initiate a free radical mechanism, leading to anti-Markovnikov addition.
**Method & Steps**:
 1. Initiation:
  Reasoning: Peroxides decompose to form free radicals.
  Formula/Rule: $ROOR \xrightarrow{heat/light} 2RO•$
 2. Propagation:
  Working: The free radical attacks the alkyne's terminal carbon (less substituted carbon) to form a more stable secondary radical intermediate. Then, HBr adds to this radical.
  Key Point: Anti-Markovnikov addition occurs due to the free radical mechanism. The Br adds to the less substituted carbon.
  $RO• + HBr ightarrow ROH + Br•$
  $Br• + C_6H_5C≡CCH_3 ightarrow C_6H_5C(Br)=CHCH_3$
 3. Termination:
  Result: The major product is 2-Bromo-1-phenylpropene.
  Verification: The reaction follows the anti-Markovnikov rule due to the presence of peroxides.
 ## OPTION ANALYSIS
A :x: 1-Bromo-1-phenylpropene: This would be the product of Markovnikov addition, which is not favored in the presence of peroxides.
B ✓: 2-Bromo-1-phenylpropene: This is the correct product formed via anti-Markovnikov addition.
C :x: 1-Bromo-1-phenylpropane: This implies addition of HBr across the triple bond with subsequent reduction, which doesn't occur under these conditions.
D :x: 2-Bromo-1-phenylpropane: This is also incorrect; it suggests addition of HBr across the triple bond with reduction, which is not observed in this reaction.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Applying Markovnikov's rule in the presence of peroxides: Remember that peroxides initiate a free radical mechanism that leads to anti-Markovnikov addition.
  2.Incorrectly predicting the radical intermediate stability: The more substituted radical is more stable, but the initial attack is on the less substituted carbon in this free radical reaction.
 **Quick Tips**:
  1.In the presence of peroxides with HBr and alkynes, expect anti-Markovnikov addition.
  2.Remember that free radical reactions follow a different regioselectivity than ionic additions.

THIRUPATHI REDDY · Answer

1-Bromo-1-phenylpropene

THIRUPATHI REDDY · Answer

The correct Option is "2-Bromo-1-phenylpropene"

THIRUPATHI REDDY · Answer

1-Bromo-1-phenylpropane

THIRUPATHI REDDY · Answer

2-Bromo-1-phenylpropane

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