Arrange the following sets of compounds in order of their increasing boiling points.
A. Pentan-1-ol
B. Butan-1-ol
C. Butan-2-ol
D. Ethanol
E. Propan-1-ol
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → D < E < C < B < A
All five are alcohols with intermolecular hydrogen bonding; boiling point rises with the number of carbon atoms and, for isomers, falls with branching. Placing each, lowest first:
D. Ethanol — first, 351 K. Two carbon atoms.
E. Propan-1-ol — second, 370 K. Three carbon atoms.
C. Butan-2-ol — third, 373 K. Four carbon atoms, but branched, so below butan-1-ol.
B. Butan-1-ol — fourth, 391 K. Four carbon atoms in a straight chain.
A. Pentan-1-ol — last, 411 K. Five carbon atoms.
NCERT (2026-27 edition):
Boiling Points – “The boiling points of alcohols and phenols increase with increase in the number of carbon atoms (increase in van der Waals forces). In alcohols, the boiling points decrease with increase of branching in carbon chain (because of decrease in van der Waals forces with decrease in surface area).”