What is the main product of the reaction between 2 - methyl propene with HBr ?

Options

A. 1 - bromo butane
B. 1 - bromo-2 methyl propane
C. 2- bromo butane
D. 2 - bromo - 2methyl propane

Answer

To determine the main product of the reaction between 2-methylpropene and HBr, we can follow these steps:

### Step 1: Identify the Structure of 2-Methylpropene
2-methylpropene is an alkene with the following structure:
```
CH3
|
CH2=C
|
CH3
```
This compound has a double bond between the second and third carbon atoms.

**Hint:** Remember that the presence of a double bond in alkenes makes them reactive towards electrophiles like HBr.

### Step 2: Understand the Reaction with HBr
When 2-methylpropene reacts with HBr, the HBr molecule will dissociate into H⁺ and Br⁻ ions. The H⁺ ion will act as an electrophile and will add to one of the carbon atoms involved in the double bond.

**Hint:** Electrophiles are species that seek electrons and will attack regions of high electron density, such as double bonds.

### Step 3: Determine the Possible Carbocation Formation
There are two ways the double bond can break:
1. The H⁺ can add to the first carbon (C1), leading to a carbocation at C2.
2. The H⁺ can add to the second carbon (C2), leading to a carbocation at C3.

However, the stability of the carbocations formed will determine which pathway is favored.

**Hint:** More stable carbocations are formed from more substituted carbons due to hyperconjugation and inductive effects.

### Step 4: Analyze Carbocation Stability
1. If H⁺ adds to C1, the resulting carbocation (C2) is a secondary carbocation (more stable).
2. If H⁺ adds to C2, the resulting carbocation (C3) is a primary carbocation (less stable).

Since secondary carbocations are more stable than primary carbocations, the reaction will proceed via the formation of the secondary carbocation.

**Hint:** Always compare the stability of carbocations; tertiary > secondary > primary.

### Step 5: Nucleophilic Attack by Br⁻
Once the more stable secondary carbocation is formed, the Br⁻ ion will act as a nucleophile and attack the positively charged carbon (C2).

**Hint:** Nucleophiles are attracted to positively charged centers, so they will readily react with carbocations.

### Step 6: Identify the Product
The final product after the nucleophilic attack will be:
```
CH3
|
CH2—Br
|
CH3
```
This compound is named 2-bromo-2-methylpropane.

**Hint:** Naming conventions follow the IUPAC rules, where the position of the substituent (Br) and the longest carbon chain are considered.

### Conclusion
The main product of the reaction between 2-methylpropene and HBr is **2-bromo-2-methylpropane**.

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