Question:
Which of the following isomers of \(\text{C}_4\text{H}_9\text{OH}\) has lowest boiling point ?
Which of the following isomers of \(\text{C}_4\text{H}_9\text{OH}\) has lowest boiling point ?
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More branching means a smaller surface area, weaker van der Waals forces and a lower boiling point.
Updated On: Oct 1, 2026
- n - Butyl alcohol
- Isobutyl alcohol
- sec-Butyl alcohol
- tert Butyl alcohol
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
All four are isomers of \(\text{C}_4\text{H}_9\text{OH}\), so they have the same molar mass and can all form hydrogen bonds. The difference in boiling point comes from the shape of the molecule.
Step 2: Key Formula or Approach:
Among isomers, a more branched molecule is more compact. Smaller surface area means weaker van der Waals forces and so a lower boiling point.
Step 3: Detailed Explanation:
n-Butyl alcohol is a straight chain, with the largest surface area, and boils at about 118 degrees C.
Isobutyl alcohol has one branch near the end of the chain and boils at about 108 degrees C.
sec-Butyl alcohol has the OH on a secondary carbon and boils at about 99 degrees C.
tert-Butyl alcohol is the most branched and almost spherical, and boils at about 83 degrees C.
The order of boiling point is primary > secondary > tertiary for isomeric alcohols.
Final Answer:
tert-Butyl alcohol has the lowest boiling point, option (D). \[ \boxed{\text{tert-Butyl alcohol (D)}} \]
All four are isomers of \(\text{C}_4\text{H}_9\text{OH}\), so they have the same molar mass and can all form hydrogen bonds. The difference in boiling point comes from the shape of the molecule.
Step 2: Key Formula or Approach:
Among isomers, a more branched molecule is more compact. Smaller surface area means weaker van der Waals forces and so a lower boiling point.
Step 3: Detailed Explanation:
n-Butyl alcohol is a straight chain, with the largest surface area, and boils at about 118 degrees C.
Isobutyl alcohol has one branch near the end of the chain and boils at about 108 degrees C.
sec-Butyl alcohol has the OH on a secondary carbon and boils at about 99 degrees C.
tert-Butyl alcohol is the most branched and almost spherical, and boils at about 83 degrees C.
The order of boiling point is primary > secondary > tertiary for isomeric alcohols.
Final Answer:
tert-Butyl alcohol has the lowest boiling point, option (D). \[ \boxed{\text{tert-Butyl alcohol (D)}} \]
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