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Boiling point is defined as the actual temperature required to bring a liquid substance to a boil and thus boiling is a chemical process demonstrated by a liquid once it attains temperature required for vaporization. Butanoic acid and the 2-pentanone are liquids and therefore posses their respective boiling points. Butanoic acid (C4H8O2) boils at 1640C (Arun 2005, pg 939) while 2-pentanone (C5H10O) boils at 101-1050C (Arun 2005, pg 422). Therefore it is evident that the carboxylic acid member, the Butanoic acid, has got higher boiling point. This is brought about by the differences in their molecular structures and types of intermolecular bonds.

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Figure: Butanoic acid Structural formula

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Figure: 2-pentanone structural formula

Several factors affect boiling points of substance. Pressure, molecular structure and the purity of a liquid affects its boiling point. In our case we are only looking at molecular structures, arrangement and properties since other factors such as pressure are same for the two compounds. Strong intermolecular forces result in high boiling points and the greater the number of carbons in a compound, the higher the boiling point. Branched carbons reduce the boiling point.

Butanoic acid posses three types of intermolecular bonds. The hydrogen bond due to the existence of the polar hydroxyl group (-OH), the dipole-dipole intermolecular forces that result from the polarized carbon- oxygen atoms (C=O) and the weak van der Waals dispersion forces that exist in between the carbon and hydrogen atoms (C-H). The strongest intermolecular bond is the hydrogen bond and therefore much more energy is needed to break it compared to the other two types of bonds.

The atoms of the 2-Pentanone compound are bonded with only two types of bonds. The dipole-dipole intermolecular bonds resulting from the polarized carbon-oxygen (C=O) atoms and the weak van der Waals dispersion forces existing between carbon-hydrogen (C-H) atoms. The dipole-dipole intermolecular bonds are the strongest for this compound and require less energy to break when compared with hydrogen bonds in the case of Butanoic acid.

Butanoic acid will therefore require more heat energy to break the three types of bonds to allow for boiling and vaporization to occur while 2-pentanone will require less amount of heat energy to break the bonds. Therefore the compounds (Butanoic acid) that require more amounts of heat energy to break the bonds certainly will have high boiling points and therefore the reason why Butanoic acid has got higher boiling point when compared to 2-Pentanone.


BAHL, A., & BAHL, B. S. (2005). A textbook of organic chemistry (for B.Sc. students). New Delhi, S. Chand.

MANNING, P. (2009). Chemical bonds. New York, Chelsea House.

PAULING, L. (1960). The nature of the chemical bond and the structure of molecules and crystals: an introduction to modern structural chemistry. Ithaca, N.Y., Cornell University Press.

HUGGINS, M. L. (1920). Chemical bonds. Thesis (M.S. in Chemistry)—University of California, Berkeley, May 1920.