Question: Rank the following isomers in order of increasing boiling point, and explain the reasons for your order of ranking.

The boiling point of compounds is dependent on the molecular weight, intermolecular attractive forces and family of a compound from which it belongs.With an increase in molar mass, the boiling point increases and the more the hydrogen bonding, the higher the boiling point.

• The given isomers are n-pentanol, ethyl acetate and valeric acid. These have different functional groups.
• The carboxylic acid group (-COOH) is present in valeric acid.
• In n-pentanol, the alcohol group (-OH) is present.
• In ethyl acetate, the ester group (-COO) is present.

The boiling point for ethyl acetate (ester-containing compound) is the lowest (77⁰C) because ester does not form hydrogen bonds. Then comes n-pentanol (alcohol-containing compound), which forms hydrogen bonds, so it has a higher boiling point (138⁰C) than ethyl acetate. At last, valeric acid (carboxylic acid-containing compound) forms two hydrogen bonds and boils in the form of a dimer. So, it has the highest boiling point among all (186⁰C)). Thus, the order of increasing boiling point is,

Order of increasing boiling point