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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.

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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.

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    $\begingroup$ Same reason why n-Butane has a higher boiling point than Isobutane: More intermolecular van der Waals interaction. $\endgroup$
    – Karl
    Sep 26, 2015 at 9:59

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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.

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  • $\begingroup$ Structuring and packing is usually an argument when talking about the melting point, right? How relevant would it be for liquid $\to$ gas? $\endgroup$ Mar 6, 2019 at 14:26
  • $\begingroup$ There is higher energy needed to get away from liquid. $\endgroup$
    – Poutnik
    May 21, 2019 at 5:42

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