For the given reaction how many products are optically active (all isomers) :
`CH_3-undersetunderset(CH_3)(|)oversetoverset(CH_3)(|)C-CH_2-oversetoverset(CH_3)(|)CH-CH_3overset(Br_2//h upsilon)to`

Answer

To determine how many products from the given reaction are optically active, we will follow these steps:

### Step 1: Identify the Reactant Structure
The reactant is a branched alkane with multiple methyl groups. The structure can be represented as:
```
CH3
|
CH3 - C - CH2 - C - CH3
|
CH3
```
This compound is 2,2,4-trimethylpentane.

### Step 2: Understand the Reaction Conditions
The reaction involves the bromination of the alkane in the presence of light (indicating a free radical mechanism). This means that bromine will substitute hydrogen atoms at various positions on the carbon chain.

### Step 3: Identify Possible Bromination Sites
The possible sites for bromination in 2,2,4-trimethylpentane are:
1. The first carbon (C1)
2. The second carbon (C2)
3. The third carbon (C3)
4. The fourth carbon (C4)

### Step 4: Determine the Products
1. **Bromination at C1**:
- Product: 1-bromo-2,2,4-trimethylpentane
- Chiral Centers: None (no carbon with four different groups)

2. **Bromination at C2**:
- Product: 2-bromo-2,4-trimethylpentane
- Chiral Centers: One (C2 has four different groups: Br, CH3, CH3, and the rest of the carbon chain)
- Optical Activity: Yes, has D and L isomers (2 optically active)

3. **Bromination at C3**:
- Product: 3-bromo-2,2,4-trimethylpentane
- Chiral Centers: None (C3 has two CH3 groups and two H atoms)

4. **Bromination at C4**:
- Product: 4-bromo-2,2,4-trimethylpentane
- Chiral Centers: One (C4 has four different groups: Br, CH3, CH2, and the rest of the carbon chain)
- Optical Activity: Yes, has D and L isomers (2 optically active)

### Step 5: Count the Optically Active Products
From the analysis:
- From bromination at C2: 2 optically active isomers
- From bromination at C4: 2 optically active isomers
- Total optically active products = 2 + 2 = 4

### Final Answer
**Total number of optically active products: 4**

---