Organic Chemistry: Hexanal and 1-Heptanol Boiling Point Analysis

This report provides a comparative analysis of the boiling points of Hexanal and 1-Heptanol, two organic compounds. The report begins by stating the observed boiling points for each compound, with 1-heptanol having a significantly higher boiling point than hexanal. The core of the report explains the differences in boiling points based on the molecular structures and intermolecular forces present in each compound. Specifically, the report highlights the role of hydrogen bonding in 1-heptanol, where the oxygen atom is directly bonded to a hydrogen atom, leading to strong intermolecular forces. Conversely, hexanal exhibits dipole-dipole interactions due to the presence of a polar C=O bond. The report concludes that the stronger hydrogen bonds in 1-heptanol result in a higher boiling point compared to the weaker dipole-dipole forces in hexanal. The report also mentions the molecular masses of the two compounds to emphasize the impact of intermolecular forces on boiling points.

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The boiling point of Hexanal is 126.9 oC while the boiling point of 1-heptanol is 178.5 0C
(Haynes, 2014). 1-heptanol has a higher boiling point than hexanal. The difference in the boiling
points can be explained in terms of the molecular structures of the two compounds and the nature
of the intermolecular forces of attraction between the molecules.
The molecular formula of Hexanal is C6H12O and its molecular mass is 100.16 g/mol
(Haynes, 2014). The molecular formula of 1-heptanol is C7H16O and its molecular mass is
116.20 g/mol. The structures are as shown below.
Hexanal
1-Heptanol
The boiling points of organic compounds increase with the increase in the molecular
weights. 1-Heptanol has one carbon more than hexanal hence is expected to have a slightly
higher boiling point. Since the molecular masses of the two compounds are comparable, it is
expected that their boiling points are almost similar. However, this is not the case as 1-Heptanol
has a much higher boiling point (178.5 oC) compared to hexanal (126.9 oC). The difference is
attributed to the nature of the intermolecular forces of the molecules.
In 1-Heptanol, the oxygen atom is directly bonded to a hydrogen atom. Since oxygen is
highly electronegative, the O-H bond is very polar; with the oxygen end acquiring a partial
negative charge and the H end being partially positive. The oxygen atom of one molecule attracts
the Hydrogen molecule of a neighboring molecule leading to formation of Hydrogen bonding

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between the molecules. Hydrogen bonds are the strongest inter-molecular forces and require a lot
of energy to overcome hence the unusually high boiling point of 1-heptanol.
In Hexanal, the Oxygen atom is not bonded directly to a hydrogen atom hence no
hydrogen bonding between molecules. The oxygen atom forms a double bond with carbon.
Since O is more electronegative than C, the O=C bond is highly polar, with the Oxygen end
acquiring a partial negative charge and the Carbon end a partial positive charge thus, forming a
permanent dipole. The dipole of one molecule attracts the oppositely charged end of another
molecule leading to formation of dipole-dipole attractions between molecules. The dipole-dipole
forces are relatively strong, giving hexanal a significantly higher boiling point compared to other
organic molecules of the comparable mass. However, these forces are not as strong as hydrogen
bonds and thus explain why the boiling point of hexanal is lower than that of 1-heptanol.

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References
Haynes, W. M. (2014). CRC handbook of chemistry and physics. Boca Raton, FL: CRC
Press.