An alkane by molecular weight 72 upon chlorination gives one monochlorination product. The alkane is

Options

A. pentane
B. 2- methylbutane
C. 2,2- dimethylpropane
D. all the of the above

Answer

To solve the problem, we need to identify the alkane with a molecular weight of 72 that produces only one monochlorination product upon chlorination.

**Step 1: Determine the molecular formula of the alkane.**
The molecular weight of the alkane is given as 72 g/mol. Alkanes have the general formula CnH(2n+2).

**Step 2: Calculate the number of carbon atoms (n).**
Using the molecular formula:
- The molecular weight of carbon (C) is approximately 12 g/mol.
- The molecular weight of hydrogen (H) is approximately 1 g/mol.

Let’s denote the number of carbon atoms as n. The molecular weight of the alkane can be expressed as:
\[ \text{Molecular weight} = 12n + (2n + 2) \]
\[ 72 = 12n + 2n + 2 \]
\[ 72 = 14n + 2 \]
\[ 70 = 14n \]
\[ n = 5 \]

**Step 3: Write the molecular formula for the alkane.**
If n = 5, then the molecular formula is C5H(2*5 + 2) = C5H12. This corresponds to pentane.

**Step 4: Analyze the chlorination process.**
Chlorination of alkanes can lead to the formation of multiple products depending on the structure of the alkane. However, for the alkane to give only one monochlorination product, it must be symmetrical.

**Step 5: Identify the symmetrical alkane.**
The symmetrical alkane with the formula C5H12 is 2,2-dimethylpropane (C5H12). This structure allows for only one type of hydrogen atom to be replaced by chlorine, resulting in only one monochlorination product.

**Step 6: Conclusion.**
Thus, the alkane that fits the criteria of having a molecular weight of 72 and yielding only one monochlorination product upon chlorination is 2,2-dimethylpropane.

**Final Answer: 2,2-dimethylpropane (C5H12)**