What product (s) is (are) obtained when 2 - bromobutane undergoes an elimination reaction with a strong base ?

Options

A. Only 1 - butene
B. Only 2 - butene
C. 1 - butene and 2 - butene , with more 1 - butene
D. 1 - butene and 2 - butene , with more 2 - butene

Answer

To determine the products obtained when 2-bromobutane undergoes an elimination reaction with a strong base, we can follow these steps:

### Step 1: Identify the structure of 2-bromobutane
2-bromobutane is a four-carbon alkyl halide with a bromine atom attached to the second carbon. Its structure can be represented as follows:

```
CH3-CH-CH2-CH3
|
Br
```

### Step 2: Understand the elimination reaction
An elimination reaction involves the removal of a leaving group (in this case, bromine) and a hydrogen atom from adjacent carbon atoms, leading to the formation of a double bond. A strong base, such as alcoholic KOH, is typically used to facilitate this reaction.

### Step 3: Identify the β-hydrogens
In 2-bromobutane, the carbon atoms adjacent to the carbon bonded to bromine (the α-carbon) are the β-carbons. The β-carbons are the second and third carbons in the chain.

### Step 4: Determine the possible products
When a strong base removes a hydrogen atom from a β-carbon, two possible alkenes can be formed:

1. **1-butene**: This product is formed when a hydrogen atom is removed from the β-carbon adjacent to the α-carbon (the first carbon). The structure is:

```
CH2=CH-CH2-CH3
```

2. **2-butene**: This product is formed when a hydrogen atom is removed from the other β-carbon (the third carbon). The structure is:

```
CH3-CH=CH-CH3
```

### Step 5: Analyze the stability of the products
2-butene is more stable than 1-butene due to the presence of more alkyl substituents around the double bond (it has more α-hydrogens). Therefore, 2-butene is the major product, while 1-butene is the minor product.

### Conclusion
The products obtained from the elimination reaction of 2-bromobutane with a strong base are:
- **1-butene** (minor product)
- **2-butene** (major product)

### Final Answer
1-butene and 2-butene are the products obtained when 2-bromobutane undergoes an elimination reaction with a strong base.

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