How many alkanes (only structural isomers) are possible with the molecular formula `C_(4)H_(8)`

Options

A. 4
B. 3
C. 5
D. 6

Answer

To determine how many structural isomers of alkanes are possible with the molecular formula C₄H₈, we will analyze the different structural arrangements that can be formed with this formula.

### Step-by-Step Solution:

1. **Identify the Molecular Formula**:
The molecular formula given is C₄H₈. This indicates that we are dealing with a hydrocarbon that contains 4 carbon atoms and 8 hydrogen atoms.

2. **Determine the Type of Compounds**:
Since the question specifically asks for alkanes, we need to recognize that C₄H₈ is not a saturated alkane (which would have the formula C₄H₁₀). Instead, C₄H₈ can represent alkenes or cycloalkanes. However, we will focus on structural isomers that can be classified as alkenes.

3. **Identify Possible Structural Isomers**:
We can derive the following structural isomers for C₄H₈:

- **1-Butene**: CH₂=CH-CH₂-CH₃
- **2-Butene**: CH₃-CH=CH-CH₃ (can exist in cis and trans forms, but they are not counted separately as structural isomers)
- **Isobutylene (or 2-methylpropene)**: CH₂=C(CH₃)-CH₃
- **Cyclobutane**: A cyclic structure with four carbon atoms (C₄H₈)
- **Methylcyclopropane**: A cyclopropane ring with a methyl group attached (C₃H₆ with a CH₃ group)

4. **Count the Unique Structural Isomers**:
From the above analysis, we can list the unique structural isomers:
- 1-Butene
- 2-Butene
- Isobutylene
- Cyclobutane
- Methylcyclopropane

Thus, we find that there are **5 structural isomers** for the molecular formula C₄H₈.

5. **Conclusion**:
Therefore, the answer to the question is that there are **5 structural isomers** possible for the molecular formula C₄H₈.

### Final Answer:
The number of structural isomers possible with the molecular formula C₄H₈ is **5**.

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