3 - Methylpent -2- ene `overset(HBr)underset(H_(2)O_(2))rarrZ`.
The number of stereoisomers possible for the product 'Z' is _______.

Answer

To solve the problem, we will follow these steps:

### Step 1: Identify the structure of 3-methylpent-2-ene
3-methylpent-2-ene has a chain of 5 carbon atoms with a double bond between the second and third carbon atoms. The structure can be represented as follows:

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

### Step 2: Understand the reaction with HBr in the presence of H2O2
In the presence of hydrogen peroxide (H2O2), the addition of HBr occurs via a free radical mechanism. This means that the bromine atom will preferentially add to the less substituted carbon atom (anti-Markovnikov addition).

### Step 3: Determine the product 'Z'
When HBr adds to 3-methylpent-2-ene in the presence of H2O2, the bromine will attach to the second carbon (less substituted), and a hydrogen will attach to the third carbon. The product formed is 2-bromo-3-methylpentane:

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

### Step 4: Identify chiral centers in the product
To find the number of stereoisomers, we need to identify the chiral centers in the product. A chiral center is a carbon atom that has four different groups attached to it.

1. The second carbon (attached to Br) has:
- CH3 (methyl group)
- CH2-CH3 (ethyl group)
- H (hydrogen)
- Br (bromine)
This carbon is a chiral center.

2. The third carbon (attached to H) has:
- CH3 (methyl group)
- CH2-CH3 (ethyl group)
- H (hydrogen)
- Br (bromine)
This carbon is also a chiral center.

### Step 5: Calculate the number of stereoisomers
The number of stereoisomers can be calculated using the formula:
\[ \text{Number of stereoisomers} = 2^n \]
where \( n \) is the number of chiral centers.

In this case, we have identified 2 chiral centers (from the second and third carbons).

Thus, \( n = 2 \):
\[ \text{Number of stereoisomers} = 2^2 = 4 \]

### Conclusion
The number of stereoisomers possible for the product 'Z' is **4**.

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