n-butane on monobromination gives three isomers. The number of product(s) obtained when the major product is heated with KOH in `CH_(3)CH_(2)OH` is/are _____

Answer

To solve the problem, we need to follow these steps:

### Step 1: Understand the Structure of n-Butane
n-Butane is a straight-chain alkane with the formula C4H10. Its structure can be represented as:
\[ \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_3 \]

### Step 2: Monobromination of n-Butane
When n-butane undergoes monobromination (the substitution of one hydrogen atom with a bromine atom) in the presence of light (which initiates a free radical reaction), we can obtain three isomers:
1. **1-Bromobutane**: \[ \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2\text{Br} \]
2. **2-Bromobutane**: \[ \text{CH}_3-\text{CH}(\text{Br})-\text{CH}_2-\text{CH}_3 \] (this is a chiral center, leading to two enantiomers)
3. **3-Bromobutane**: \[ \text{CH}_3-\text{CH}_2-\text{CH}(\text{Br})-\text{CH}_3 \]

### Step 3: Identify the Major Product
Among the products, **2-Bromobutane** is the major product due to the stability of the secondary free radical formed during the bromination process.

### Step 4: Heating 2-Bromobutane with KOH in Ethanol
When 2-Bromobutane is heated with KOH in ethanol (C2H5OH), an elimination reaction occurs, resulting in the formation of alkenes. The elimination reaction can be represented as:
\[ \text{R-CH}(\text{Br})-\text{R'} + \text{KOH} \rightarrow \text{R-CH}=\text{R'} + \text{KBr} + \text{H}_2\text{O} \]

### Step 5: Determine the Possible Products
For 2-Bromobutane, the elimination can yield:
1. **But-2-ene**: This can exist as two geometric isomers due to the presence of a double bond:
- **Cis-But-2-ene**: \[ \text{CH}_3-\text{C}=\text{C}-\text{CH}_3 \] (with both methyl groups on the same side)
- **Trans-But-2-ene**: \[ \text{CH}_3-\text{C}=\text{C}-\text{CH}_3 \] (with methyl groups on opposite sides)

### Step 6: Count the Total Products
Thus, the total number of products obtained when the major product (2-Bromobutane) is heated with KOH in ethanol is:
- 1 product (But-2-ene) that has 2 geometric isomers (Cis and Trans).

So, the total number of distinct products is **3** (1 But-2-ene + 2 geometric isomers).

### Final Answer
The number of product(s) obtained when the major product is heated with KOH in CH3CH2OH is **3**.

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