Which compound has total molecular mass of 72 with three primary carbons?
Show Hint
When identifying compounds based on molecular mass and structure, consider the number of primary, secondary, and tertiary carbons, and ensure the molecular mass matches the calculation.
Step 1: Analyzing the compounds and their molecular masses.
- n-Heptane (\( \mathrm{C_7H_{16}} \)) has a molecular mass of:
\[
(7 \times 12) + (16 \times 1) = 84 \, \text{g/mol}
\]
So, n-Heptane does not have the required molecular mass of 72.
- 2,2-Dimethylbutane (\( \mathrm{C_6H_{14}} \)) has a molecular mass of:
\[
(6 \times 12) + (14 \times 1) = 74 \, \text{g/mol}
\]
So, 2,2-Dimethylbutane does not match the molecular mass of 72.
- 1,1-Dimethylcyclopropane (\( \mathrm{C_6H_{12}} \)) has a molecular mass of:
\[
(6 \times 12) + (12 \times 1) = 72 \, \text{g/mol}
\]
But it does not have three primary carbons, as the cyclopropane ring restricts the possibility of having three primary carbons.
- 2-Methylbutane (\( \mathrm{C_5H_{12}} \)) has a molecular mass of:
\[
(5 \times 12) + (12 \times 1) = 72 \, \text{g/mol}
\]
This compound also contains three primary carbon atoms (the methyl group at position 2, and two primary carbons on the butane chain).
Step 2: Conclusion.
2-Methylbutane has the correct molecular mass of 72 and has three primary carbon atoms. Therefore, the correct answer is: Final Answer: (D) 2-Methylbutane.
