An alkane (mol. Wt. 72) forms only one monochlorinated product. Its formula is

Options

A. `(CH_(3))_(4)C`
B. `CH_(3)(CH_(2))_(3)CH_(3)`
C. `(CH_(3))_(2)CHCH_(2)CH_(3)`
D.

Explanation

To solve the problem, we need to identify an alkane with a molecular weight of 72 that forms only one monochlorinated product. Here’s a step-by-step breakdown of how to arrive at the solution:

### Step 1: Determine the molecular formula of the alkane
The molecular weight of alkanes can be calculated using the formula:
\[ \text{Molecular Weight} = 12n + 1(2n + 2) \]
where \( n \) is the number of carbon atoms (C) in the alkane.

Since we know the molecular weight is 72, we can set up the equation:
\[ 12n + 1(2n + 2) = 72 \]
This simplifies to:
\[ 12n + 2n + 2 = 72 \]
\[ 14n + 2 = 72 \]
\[ 14n = 70 \]
\[ n = 5 \]

### Step 2: Write the molecular formula
Since \( n = 5 \), the alkane has 5 carbon atoms. The general formula for alkanes is \( C_nH_{2n+2} \):
\[ C_5H_{2(5)+2} = C_5H_{12} \]

### Step 3: Identify the alkane
The alkane with the formula \( C_5H_{12} \) is pentane.

### Step 4: Determine the monochlorination products
Now, we need to check if pentane can produce only one monochlorinated product. Monochlorination involves replacing one hydrogen atom with a chlorine atom.

1. **Pentane Structure**:
- Pentane can exist in different structural forms (isomers), but the straight-chain form (n-pentane) is the most straightforward for this analysis.
- The structure of n-pentane is:
\[ CH_3-CH_2-CH_2-CH_2-CH_3 \]

2. **Monochlorination**:
- If we replace any of the terminal or internal hydrogen atoms with chlorine, we can analyze the products:
- Replacing a terminal hydrogen (from CH3) will yield 1-chloropentane.
- Replacing any of the internal hydrogens (from CH2) will yield the same product due to symmetry.

### Conclusion:
Since all substitutions lead to the same product (1-chloropentane), n-pentane (C5H12) is the only alkane that meets the criteria of forming only one monochlorinated product.

### Final Answer:
The formula of the alkane is \( C_5H_{12} \).

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