Boiling Point of Compounds

This essay discusses the factors affecting the boiling point of compounds such as intermolecular forces, carbon chain length, polarity, and branching. It also lists the boiling points of 2-pentanone, butanoic acid, 2-methylpropanoic acid, and 2-hexanone. The essay concludes that the boiling point of a compound depends on various factors.

Running Head: BOILING POINT OF COMPOUNDS 1
Boiling Point of Compounds
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Introduction
A compound is identified by either its physical properties or chemical properties.
Physical properties of a subsistence are those properties which can be measured or observed
without changing the matter composition, such as the polarity, solubility, density, melting and
boiling point, odor, color, texture, appearance, etc. In this essay, boiling points of inorganic
given compounds are discussed. The boiling point of a substance is affected by the relative
strength of the intermolecular forces, the length of carbon-carbon chain and polarity (OLABS,
2018). In this essay, it discusses the literature boiling points of the given four compounds which
includes 2-pentanone, butanoic acid, 2-methylpropanoic acid, and 2-hexanone. Using theory of
boiling point the four compounds are listed from the highest boiling point to lowest.
The theory of boiling point of a compound
The process by which a liquid substances changes into gaseous state is called the boiling
point of the substance. Consequently, the liquid changes into gaseous by a process of known as
evaporation. Through evaporation process, the liquid substances transformed vapor escapes to
the surrounding (Vogel, 2013). Liquid substance changes its state to gaseous state when heat is
supplied, causing the temperature increase resulting to increase in kinetic energy in the molecule.

BOILING POINT OF COMPOUNDS
The kinetic energy (KE) as a result increases the random motion of the molecules. Because of
higher intensity, the supplied heat energy weakens the attraction force in liquid molecules which
in turn becomes free and mobile thus changing its state. Environmental atmospheric pressure
affects the boiling point of a given substance (Burrows, Holman, Parsons, Pilling, & Price,
2017).
Inorganic compounds have different boiling points depending on their physical structure
such as the molecular weight, polarity etc. The compound usual boiling point indicate the
volatility of the given compound. If the boiling point of a compound is low that means the
volatile of that compound is high, and vice versa (Mirzaei, Leonardi, & Neri, 2016). In case, the
boiling point of a substance is lower than the temperature of surrounding, then the substance
normally exist as a gas at atmospheric pressure (OLABS, 2018). Furthermore, the compound
appear as liquid or solid if the boiling point is higher (James, 2010). The general trends affecting
the boiling point are:
i) The relative strength of intermolecular forces like Vander Waals dispersion, dipole-
dipole interaction, hydrogen bonding, and ionic force do affect the boiling point of a
compound. The functional group present in the compound does influence these
intermolecular forces (Haynes, 2014). The Vander Waals dispersion is the weakest force
of attraction while ionic forces are the strongest forces of attraction (Haynes, 2014).
ii) The Length of carbon chain affect the boiling point in that as the bigger the length of
carbon-carbon chain the higher the boiling point of that compound. The reason behind is
because the force of attractions in the molecules do increase as the molecules become
longer and has more electrons (burrows, et al, 2017).

BOILING POINT OF COMPOUNDS
iii) The polarity of a given molecule affect the boiling point of that substance, the less the
polarity the lower the boiling point. The functional group of a compound determines the
polarity of that substance (Dalmaschio, et al., 2014).
iv) Branching in molecules reduces the surface area thus reducing the forces of attraction
between individual molecules, resulting to decrease the boiling point. As Van der Waals
forces increases with increase in surface area since as the length of carbon chain
increases, the compound increases surface area (Yaws, 2015). Thus, the power for
individual molecules which draw to each other increases. More carbon-carbon chains in a
molecule decreases the surface area henceforth reduces the power of force of attraction
between each molecule resulting to a decrease in boiling point (Braude & Nachod, 2013).
Results and Discussion
Table 1 below shows the physical properties of the given four (4) compounds which
includes 2-pentanone, 2-methylpropanoic acid, butanoic acid, and 2-hexanone, it indicates the
boiling point of each compound from highest to lowest boiling point.
Compound Butanoic acid Isobutyric acid 2-hexanone 2-pentanone
IUPAC name Butanoic acid 2-
methylpropanoic
acid
Hexan-2-one pentan-2-one
Chemical Formula C4H8O2 (CH3)2CHCOOH C4H9COCH3 C5H10O
Molecular Mass 90.0910 g/mol 88.1060 g/mol 100.1610 g/mol 86.1340 g/mol
Polar Surface Area 37.3 A2 37.3 A2 17.1 A2 17.1 A2
Volatility Volatile Volatile Volatile Volatile

BOILING POINT OF COMPOUNDS
Intermolecular Force strong
hydrogen
bonds
strong hydrogen
bonds
Dipole-dipole
bonds
Dipole-dipole
bonds
Boiling Point 163.50 ˚C 155.00 ˚C 127.60 ˚C 101.00 ˚C
Table 1: Physical properties of the four (4) given compounds (PubChem, 2005-2018)
Comparing the boiling point of the two acids (Butanoic acid and 2-methylpropanoic
acid). Though, they have the same Topological Polar Surface Area (37.3 A2), same element
composition and both have strong hydro-gen bonds (Table 1), Butanoic acid has a high boiling
point than 2-methylpropanoic acid. This can be illustrated by the carbon chain in functional
group in these compounds, Butanoic acid has four carbon chain while 2-methylpropanoic acid
has three (3) longest carbon chain,(as shown in figure 1) thus the longer the Carbon chain the
higher the boiling point. Furtherer more, 2-methylpropanoic acid contain a branch, thus reducing
the boiling point. The two reasons explain why Butanoic acid has a higher BP than 2-
methylpropanoic acid
Figure 1: Structure of 2-methylpropanoic acid Butanoic acid
Now, comparing the acids and the ketones, the two acids has higher boiling point that the
two ketones. Though, all are volatile and polar, the ketones has small surface area as compared

BOILING POINT OF COMPOUNDS
to acids, thus the smaller the surface ares the lower the boiling point. Also, ketones are bonded
by dipole-dipole forces and acids are bonded by strong hydrogen bonds. Hydogen bonds are
stronger than the dipole-dipole bond, resulting acids to have higher boiling poits that ketones.
Both ketones (2-hexanone and 2-pentanone) have the same Topological Polar Surface
Area (17.1 A2), same intermolecular forces and are both polar, their difference in boiling point is
brought by the carbon chain in functional group and the branching similar to acids.
Conclusions
In this essay, the trends that affect the boiling point of a substance was done by
comparing the boiling point of different compounds. It was discovered that the boiling point of a
compound depends numerous factors such as the length of carbon-carbon chain in the functional
group, strength of intermolecular forces, polarity and the branching of a compound.

BOILING POINT OF COMPOUNDS
References
Braude, E., & Nachod, F. (2013). Determination of organic structures by physical methods.
Elsevier.
Burrows, A., Holman, J., Parsons, A., Pilling, G., & Price, G. (2017). Chemistry3: Introducing
inorganic, organic and physical chemistry (2nd ed.). Oxford: Oxford University Press.
Dalmaschio, G., Malacarne, M., de Almeida, V., Pereira, T., Gomes, A., de Castro, E., . . .
Romão, W. (2014). Characterization of polar compounds in a true boiling point
distillation system using electrospray ionization FT-ICR mass spectrometry. Fuel, 115,
190-202.
Haynes, W. (2014). CRC handbook of chemistry and physics. CRC press.
James. (2010, Octomber 25). 3 Trends That Affect Boiling Points. Retrieved from Master
Organic Chemistry: https://www.masterorganicchemistry.com/2010/10/25/3-trends-that-
affect-boiling-points/
Mirzaei, A., Leonardi, S., & Neri, G. (2016). Detection of hazardous volatile organic compounds
(VOCs) by metal oxide nanostructures-based gas sensors. A review. Ceramics
International, 42(14), pp. 15119-15141.
OLABS. (2018). Boiling Point of an Organic Compound. Retrieved from Olabs:
http://amrita.olabs.edu.in/?brch=7&cnt=1&sim=111&sub=73

BOILING POINT OF COMPOUNDS
PubChem. (2005-2018). Data deposited in or computed by PubChem. Retrieved from
PubChem.com: https://pubchem.ncbi.nlm.nih.gov
Vogel, A. (2013). A text-book of practical organic chemistry including qualitative organic
analysis . London; New York; Toronto;: Longmans Green And Co.
Yaws, C. (2015). Yaws handbook of physical properties for hydrocarbons and chemicals.
Elsevier Science.