# Why does butanoic acid have a higher boiling point than isobutyric acid?

Why does butanoic acid have a higher boiling point then isobutyric acid, when they have similar molar mass and molecular structure?

Butanoic acid ($$\ce{C4H8O2}$$) has a molar mass of 88.11 g/mol, the boiling point is 163 °C, and intermolecular force of H-bond.

Isobutyric acid ($$\ce{C4H8O2}$$) has a molar mass of 88.11 g/mol, the boiling point is 155 °C, and intermolecular force of H-bond.

• Same reason why n-Butane has a higher boiling point than Isobutane: More intermolecular van der Waals interaction. – Karl Sep 26 '15 at 9:59

## 1 Answer

In general, linear chains are more easily structured and packed than branched ones. You need more energy to disturb the more relatively packed structure.This could explain why butanoic acid has a higher boiling point than isobutyric acid, and yet they are isomers.

• Structuring and packing is usually an argument when talking about the melting point, right? How relevant would it be for liquid $\to$ gas? – Eashaan Godbole Mar 6 at 14:26
• There is higher energy needed to get away from liquid. – Poutnik May 21 at 5:42