Boiling Points Of Organic Compounds And Factors Affecting Them

Factors Affecting Boiling Points

At a certain temperature, vapour pressure of a given liquid reaches a point equivalent to pressure of its surrounding. This temperature is defined as the boiling point of such a substance. Organic compounds exhibit a fascinating trend since they tend to have boiling points based upon certain characteristics particular to every organic compound. According to Burger, Baibourine, Bruno (2011 p.89), organic compounds comprises of a number of forces that keep the molecules together. These forces include bonds of either ionic, hydrogen bonding as well as van der Waal forces of attraction or the dipole to dipole moments or both. Of all the forces, it has been noted that ionic bonds provides the greatest forces of attraction hence substances possessing it considerably than other exhibit higher boiling points. After ionic forces of attraction/bonds, hydrogen bonds ranks second followed by dipole-dipole forces with the van der Waal forces of attraction being ranked as the weakest of all hence associated with lowest boiling points in substances in which it occurs compared to the aforementioned forces respectively. For instance, substances having OH groups including the carboxylic acids has been identified to have high values of boiling points when compared to substances having the COH, that is the aldehydes possessing the dipole-dipole bonds.

As per Burger et al (2011 p.121), atomic structure of the particles influences the surface zone of the atoms which thusly influences the Van der Waals scattering influences and consequently, the boiling points of the atoms. A long chain natural compound builds the surface region of the atom and the sub-atomic weight of the particle. Henceforth, the capacity of the individual particles to draw in one another is additionally expanded. The cooperation result in expanded scattering effects and along these lines higher boiling points.

Compound structure (Haynes, 2014 p.87).

Branched molecular structures anyway diminish boiling points of compounds as the surface zone will be diminished and subsequently, the scattering forces too will be debilitated.

Compound structure (Haynes, 2014 p.132)

The last sub-atomic structure viewpoint influencing boiling point of the substances is the introduction of the polar group of functionality. As indicated by Haynes (2014 p.192), an uncovered polar assembly like in the carboxylic acids expands boiling points.

The compound structure of the alcohol (Kerth, 2016 p.78).

Results (Kerth, 2016 p.108).

Name of the organic compound.	Molecular Structure.	Boiling Point.
Butanoic Acid	C4H8O2	164.30C (Royal Society of Chemists, 2015)
Pentanal	C5H10O	103.70C (Royal Society of Chemists, 2015)
Butane		-0.5?C (Cleveland and Morris, 2013)
1-butene		-6.3?C (Cleveland and Morris, 2013)

The above table summarises the trends in boiling points of the listed four compounds. Boiling points of these organic compounds depict the strength of the intermolecular forces of attraction that consist each an organic compound. Based on these strength mainly, the trends in boiling points can be understood. Other factors that contribute towards these trends include number of carbons as well as branching for a given compound. As aforementioned in the introduction, number of carbon atoms have a direct bearing on the boiling point of a compound such that an increase in number of carbon atoms leads to increase in the boiling point of a given compound. However, branching within the structure has an influence to decrease in the boiling point hence the higher the branching the lower the boiling point. In this regard therefore, I seek to discuss the trends in boiling points of the above compounds as in the section that follows.

Trends in Boiling Points of Four Compounds

In butanoic acid, which is classified as carboxylic acid, there are three notable forces maintaining the intermolecular bonds. These forces include the hydrogen bonds, dipole-dipole forces and the van der Waal forces of attraction. A combination of the three bonds precisely denotes that braking the bonds requires significant energy hence as result the boiling point of butanoic acid is high. In aldehydes and specifically the compound pentanal, the molecular structure is sustained by two forces namely; the dipole-dipole forces and the van der Waal forces of attraction (Vogel, 2013 p.86).

The hydrogen bonding in the butanoic acid molecule outcomes in the practical dissimilarity in boiling points of the butanoic acid and the pentanal as the bond needs additional energy to break when paralleled to the dipole-dipole bonds in the pentanal molecule.

While butane is unsaturated, butane is a saturated hydrocarbon with all the carbon atoms filled. Butene have lower boiling points than butane. Butane have higher molecular weight and high intermolecular forces of attraction hence has higher boiling point than butane despite butane having pi bond interactions hence the small difference.

Alkanes simply have carbon and hydrogen particles with no utilitarian gatherings, so the main intermolecular power that impacts the breaking point is London scattering powers. The more the atoms can contact one another, the more London scattering powers there are, and the higher the boiling point. s a govern, bigger particles have higher boiling (and dissolving) focuses. Consider the boiling points of progressively bigger hydrocarbons. More carbons and hydrogens implies a more prominent surface zone feasible for van der Waals association, and in this way higher boiling points. Beneath zero degrees centigrade (and at environmental weight) butane is a fluid, in light of the fact that the butane particles are held together by Van der Waals powers. Over zero degrees, in any case, the atoms increase enough warm vitality to break separated and enter the gas phase (Aryangat, 2014). The quality of intermolecular hydrogen holding and dipole-dipole associations is reflected in higher boiling points. Take a gander at the pattern for hexane (van der Waals collaborations just), 3-hexanone (dipole-dipole cooperations), and 3-hexanol (hydrogen holding). In every one of the three particles, van der Waals connections are critical. The polar ketone aggregate permits 3-hexanone to frame intermolecular dipole-dipole cooperations, notwithstanding the weaker van der Waals associations. 3-hexanol, as a result of its hydroxyl gathering, can shape intermolecular hydrogen bonds, which are more grounded yet. Of specific enthusiasm to scientists (and practically whatever else that is alive on the planet) is the impact of hydrogen holding in water. Since it can frame tight systems of intermolecular hydrogen bonds, water stays in the fluid stage at temperatures up to 100 OC notwithstanding its little size. By considering noncovalent intermolecular connections, we can likewise foresee relative dissolving focuses. The majority of similar standards apply: more grounded intermolecular collaborations result in a higher liquefying point. Ionic mixes, not surprisingly, as a rule have high softening points because of the quality of particle collaborations. Much the same as with boiling points, the nearness of polar and hydrogen-holding bunches on natural mixes by and large prompts higher boiling points (Bettelheim et al., n.d.). The extent of an atom impacts its liquefying point and in addition its boiling point, again because of expanded van der Waals communications between particles (Cleveland and Morris, 2013). 

What is diverse about melting point slants, that we don’t see with boiling point or dissolvability patterns, is the significance of a particle’s shape and its capacity of pack firmly together. Imagine yourself attempting to make a steady heap of balls in the floor. It simply doesn’t work, since circles don’t pack together well – there is almost no region of contact between each ball. It is simple, however, to make a pile of level articles like books.

A similar idea applies to how well particles pack together in a strong. The level state of sweet-smelling mixes enables them to pack productively, and hence aromatics have a tendency to have higher liquefying guides contrasted toward non-planar hydrocarbons and comparative atomic weights. Looking at the melting points of butane and butene, you can see that the additional methyl amass on toluene disturbs the particle’s capacity to pack firmly, in this way diminishing the total quality of intermolecular van der Waals powers and bringing down the boiling point.

References

Aryangat, A. (2014). The MCAT chemistry book. Los Angeles, CA: Nova Press, pp.420-429.

Bettelheim, F., Brown, W., Campbell, M., Farrell, S. and Torres, O. (n.d.). Introduction to general, organic, and biochemistry. 1st ed. p.A25.

Cleveland, C. and Morris, C. (2013). Diagrams, charts, and tables. 1st ed. Amsterdam: Elsevier, p.299.

Cyclic Combustion Variations in Dual Fuel Partially Premixed Pilot-Ignited Natural Gas Engines. (2012). 1st ed. Washington, D.C.: United States. Dept. of Energy. Office of Energy Efficiency and Renewable Energy, p.230.

Burger, J.L., Baibourine, E. and Bruno, T.J., 2011. Comparison of diesel fuel oxygenate additives to the composition-explicit distillation curve method. Part 4: alcohols, aldehydes, hydroxy ethers, and esters of butanoic acid. Energy & Fuels, 26(2), pp.1114-1123.

Haynes, W.M., 2014. CRC handbook of chemistry and physics. CRC press.

Kerth, C., 2016. Determination of volatile aroma compounds in beef using differences in steak thickness and cook surface temperature. Meat science, 117, pp.27-35.

Vogel, A.I., 2013. A text-book of practical organic chemistry including qualitative organic analysis. Longmans Green And Co; London; New York; Toronto.