Among the following statements, choose the correct statements.
A. Boiling point of alcohols increases with an increase in the number of carbon atoms.
B. In alcohols, boiling points increase with the increase of branching in the carbon chain.
C. Boiling points of alcohols are lesser in comparison to haloalkanes of comparable molecular mass.
D. Boiling points of alcohols are higher in comparison to hydrocarbons of comparable molecular mass.
E. The high boiling points of alcohols are mainly due to the presence of intermolecular hydrogen bonding.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, D, and E only
(A) Boiling point of alcohols increases with increase in the number of carbon atoms — True. The van der Waals forces increase as the molecules get bigger.
(B) In alcohols, boiling points increase with increase of branching in carbon chain — False. Branching decreases the surface area and the van der Waals forces, so the boiling point decreases.
(C) Boiling points of alcohols are lesser in comparison to haloalkanes of comparable molecular mass — False. Alcohols boil higher than haloalkanes, hydrocarbons and ethers of comparable molecular mass.
(D) Boiling points of alcohols are higher in comparison to hydrocarbons of comparable molecular mass — True. For example, ethanol (46 u) boils at 351 K and propane (44 u) at 231 K.
(E) The high boiling points of alcohols are mainly due to the presence of intermolecular hydrogen bonding — True. The O–H groups of neighbouring molecules are joined by hydrogen bonds, which hydrocarbons and haloalkanes lack.
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).
It is interesting to note that boiling points of alcohols and phenols are higher in comparison to other classes of compounds, namely hydrocarbons, ethers, haloalkanes and haloarenes of comparable molecular masses. For example, ethanol and propane have comparable molecular masses but their boiling points differ widely. The boiling point of methoxymethane is intermediate of the two boiling points.
The high boiling points of alcohols are mainly due to the presence of intermolecular hydrogen bonding in them which is lacking in ethers and hydrocarbons.”