Br2 H20 CH3CH,CH,CCH,Br CH,CH,CH,C=CH

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Draw the mechanism for the following reaction: Hint: the addition Br2/H2O to alkynes follows an analogous pathway as with the alkenes.

 

### Reaction of Propyne with Bromine in Water

**Reactants and Conditions**:
- **Reactant**: Propyne (CH₃CH₂C≡CH)
- **Reagents**: Bromine (Br₂) in water (H₂O)

**Reaction**:
Propyne reacts with bromine in the presence of water to form a bromo-ketone.

**Chemical Equation**:
\[ \text{CH}_3\text{CH}_2\text{C}\equiv\text{CH} \xrightarrow{\text{Br}_2/\text{H}_2\text{O}} \text{CH}_3\text{CH}_2\text{CH}_2\text{CO}\text{CH}_2\text{Br} \]

**Explanation**:
In this reaction, the alkyne (C≡C triple bond) in propyne undergoes halogenation in the presence of water. Bromine (Br₂) adds to the alkyne, and water assists in the formation of the bromo-ketone product. This type of reaction is characteristic of alkyne and involves the following steps:

1. **Addition of Bromine**: The alkyne reacts with bromine, breaking the triple bond. Here, the bromine molecule splits into two bromine atoms.

2. **Hydration/Addition of Water**: Water molecules then participate in the reaction, adding to one of the carbons, replacing one of the bromine atoms to form a carbonyl group (=O).

**Product**:
- The final product is 4-bromobut-2-one (CH₃CH₂CH₂COCH₂Br).

### Important Concepts:

- **Regioselectivity**: The addition of bromine and water to the alkyne is regioselective, leading to the formation of a bromo-ketone.
- **Mechanism**: The reaction mechanism typically involves the formation of a bromonium ion intermediate, followed by nucleophilic attack by water.

This reaction is an example of how alkynes can be transformed into more complex compounds using halogenation in aqueous solutions.
Transcribed Image Text:### Reaction of Propyne with Bromine in Water **Reactants and Conditions**: - **Reactant**: Propyne (CH₃CH₂C≡CH) - **Reagents**: Bromine (Br₂) in water (H₂O) **Reaction**: Propyne reacts with bromine in the presence of water to form a bromo-ketone. **Chemical Equation**: \[ \text{CH}_3\text{CH}_2\text{C}\equiv\text{CH} \xrightarrow{\text{Br}_2/\text{H}_2\text{O}} \text{CH}_3\text{CH}_2\text{CH}_2\text{CO}\text{CH}_2\text{Br} \] **Explanation**: In this reaction, the alkyne (C≡C triple bond) in propyne undergoes halogenation in the presence of water. Bromine (Br₂) adds to the alkyne, and water assists in the formation of the bromo-ketone product. This type of reaction is characteristic of alkyne and involves the following steps: 1. **Addition of Bromine**: The alkyne reacts with bromine, breaking the triple bond. Here, the bromine molecule splits into two bromine atoms. 2. **Hydration/Addition of Water**: Water molecules then participate in the reaction, adding to one of the carbons, replacing one of the bromine atoms to form a carbonyl group (=O). **Product**: - The final product is 4-bromobut-2-one (CH₃CH₂CH₂COCH₂Br). ### Important Concepts: - **Regioselectivity**: The addition of bromine and water to the alkyne is regioselective, leading to the formation of a bromo-ketone. - **Mechanism**: The reaction mechanism typically involves the formation of a bromonium ion intermediate, followed by nucleophilic attack by water. This reaction is an example of how alkynes can be transformed into more complex compounds using halogenation in aqueous solutions.
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