Reaction of hydrogen bromide with propene in the absence of peroxide is a/an

Options

A. free radical addition
B. nucleophilic addition
C. electrophilic substitution
D. electrophilic addition

Answer

To determine the type of reaction that occurs when hydrogen bromide (HBr) reacts with propene (C3H6) in the absence of peroxide, we can follow these steps:

### Step 1: Identify the Reactants
The reactants in this reaction are propene (C3H6) and hydrogen bromide (HBr). Propene has a double bond between two carbon atoms.

### Step 2: Understand the Mechanism of the Reaction
In the absence of peroxide, the reaction follows Markovnikov's rule. This means that the hydrogen atom from HBr will attach to the carbon atom of the double bond that has the greater number of hydrogen atoms already attached (the less substituted carbon).

### Step 3: Protonation of the Alkene
The double bond in propene acts as a nucleophile and attacks the electrophilic hydrogen (H+) from HBr. This results in the formation of a carbocation.

- The double bond in propene can be represented as CH2=CH-CH3.
- When H+ adds to one of the carbons, it creates a carbocation at the other carbon.

### Step 4: Carbocation Stability
There are two possible carbocations that can form:
1. A primary carbocation (less stable) if H+ adds to the terminal carbon (CH2).
2. A secondary carbocation (more stable) if H+ adds to the middle carbon (CH).

Since the secondary carbocation is more stable due to hyperconjugation and inductive effects, it will be the favored intermediate.

### Step 5: Nucleophilic Attack by Bromide Ion
After the formation of the more stable carbocation, the bromide ion (Br-) will attack the positively charged carbon atom, leading to the formation of the final product.

### Step 6: Final Product
The final product of the reaction is 2-bromopropane (C3H7Br), where the bromine atom is added to the more substituted carbon atom of the original double bond.

### Conclusion
The reaction of hydrogen bromide with propene in the absence of peroxide is an electrophilic addition reaction.