Question

Which of the following isomers of \(\text{C}_4\text{H}_9\text{OH}\) has lowest boiling point ?

• A. n - Butyl alcohol
• B. Isobutyl alcohol
• C. sec-Butyl alcohol
• D. tert Butyl alcohol

Hint:

More branching means a smaller surface area, weaker van der Waals forces and a lower boiling point.

Answer 1

The Correct Option is D

Step 1: Same formula, different shape:
All four isomers have one OH group, so hydrogen bonding is available to each. The deciding factor is how closely molecules can pack and touch.

Step 2: Rank by compactness:
Straight chain (n-butyl): most contact, so strongest dispersion forces, highest boiling point (about 118 degrees C).
Isobutyl: about 108 degrees C.
sec-Butyl: about 99 degrees C.
tert-Butyl: a compact ball with the OH shielded by three methyls, so the least contact, lowest boiling point (about 83 degrees C).

Step 3: Answer:
Option (D).

Final Answer:
tert-Butyl alcohol boils lowest. \[ \boxed{\text{tert-Butyl alcohol (D)}} \]