Predict the number of stereoisomers for `2,5` heptadiene.

Options

A. 4
B. 3
C. 2
D. 5

Explanation

To predict the number of stereoisomers for 2,5-heptadiene, we can follow these steps:

### Step 1: Understand the structure of 2,5-heptadiene
2,5-heptadiene indicates that there are 7 carbon atoms (hepta) and two double bonds (diene) located at the 2nd and 5th positions.

### Step 2: Draw the structure
We can draw the structure of 2,5-heptadiene as follows:
```
H H H H H
| | | | |
H--C==C--C--C==C--C--C--H
| | | | |
H H H H H
```
This structure shows the two double bonds located at the 2nd and 5th carbon atoms.

### Step 3: Identify the possibility of stereoisomerism
Stereoisomers arise due to the presence of double bonds, which can have cis (Z) and trans (E) configurations.

### Step 4: Count the double bonds
In 2,5-heptadiene, we have two double bonds. Each double bond can potentially give rise to stereoisomers:
- The double bond at position 2 can be either cis or trans.
- The double bond at position 5 can also be either cis or trans.

### Step 5: Apply the formula for stereoisomers
For compounds with multiple double bonds, the number of stereoisomers can be calculated using the formula:
\[ \text{Number of stereoisomers} = 2^n \]
where \( n \) is the number of double bonds that can exhibit geometrical isomerism.

However, since we have two double bonds, we must consider the symmetry and the fact that the terminal groups are the same.

### Step 6: Calculate the number of stereoisomers
Using the formula for geometrical isomerism:
\[ \text{Number of geometrical isomers} = 2^{n-1} + 2^{n-2} \]
where \( n \) is the number of double bonds.

For 2,5-heptadiene:
- \( n = 2 \) (two double bonds)

Substituting into the formula:
\[ \text{Number of stereoisomers} = 2^{2-1} + 2^{2-2} = 2^1 + 2^0 = 2 + 1 = 3 \]

### Conclusion
Thus, the total number of stereoisomers for 2,5-heptadiene is 3.