How many stereoisomers does this molecule have ?
`CH_3CH=CHCH_2CHBrCH_3`

Options

A. 8
B. 2
C. 4
D. 6

Answer

To determine the number of stereoisomers for the molecule `CH3CH=CHCH2CHBrCH3`, we need to follow these steps:

### Step 1: Identify the structure of the molecule
The molecular formula indicates that we have a six-carbon chain with a double bond and a bromine substituent. The structure can be drawn as follows:

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

### Step 2: Identify stereocenters
A stereocenter (or chiral center) is typically a carbon atom that has four different substituents. In this molecule, we need to check for any sp³ hybridized carbon atoms that meet this criterion.

- The carbon atom bonded to Br (C5) is sp³ hybridized and has the following substituents:
- CH3 (from C4)
- H (hydrogen)
- CH2 (from C6)
- Br (bromine)

Since all four substituents are different, C5 is a stereocenter.

### Step 3: Identify the double bond and its stereochemistry
The double bond between C2 and C3 can also give rise to stereoisomers. The two possible configurations around a double bond are cis (same side) and trans (opposite sides).

### Step 4: Count the stereoisomers
For a molecule with one stereocenter and one double bond, we can use the formula:
\[ \text{Number of stereoisomers} = 2^n \]
where \( n \) is the number of stereocenters.

In our case:
- We have one stereocenter (C5).
- The double bond (C2-C3) can have two configurations (cis and trans).

Thus, the total number of stereoisomers can be calculated as:
- For the stereocenter: 2 possibilities (R and S)
- For the double bond: 2 possibilities (cis and trans)

Combining these, we have:
\[ \text{Total stereoisomers} = 2 \times 2 = 4 \]

### Conclusion
The molecule `CH3CH=CHCH2CHBrCH3` has a total of **4 stereoisomers**.

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