Question

Which of the following compounds has the highest boiling point?

• A. \(\text{CH}_{3}\text{-CH}_{2}\text{-CH}_{3}\)
• B. \(\text{CH}_{3}\text{-CN}\)
• C. \(\text{CH}_{3}\text{-Cl}\)
• D. \(\text{CH}_{3}\text{-O-CH}_{3}\)

Hint:

For compounds of similar molar mass, the stronger the dipole-dipole attraction, the higher the boiling point.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
Boiling point rises with stronger intermolecular forces. The four compounds have similar molar masses, so polarity decides the order.

Step 2: Compare the compounds
Propane is non-polar and has only weak dispersion forces.
\(\text{CH}_3\text{Cl}\) and \(\text{CH}_3\text{OCH}_3\) are only moderately polar.
\(\text{CH}_3\text{CN}\) has the highly polar \(\text{C}\equiv\text{N}\) group and a very large dipole moment.

Step 3: Result
The strong dipole-dipole attraction in \(\text{CH}_3\text{CN}\) makes it a liquid boiling at about 82 degrees Celsius, far higher than the others.

Final Answer:
Methyl cyanide has the highest boiling point, which is option (B). \[ \boxed{\text{(B) }\text{CH}_{3}\text{-CN}} \]