Intermolecular Forces

The trends in physical properties of organic compounds such as boiling points and melting points can be deducted from their structures, including size (molecular weight, surface area), shape and functional groups. These factors significantly influence the strength of the intermolecular forces of attraction present; and the nature and strength of intermolecular forces determine the variations in boilingpoints of organic compounds. The boiling point of a liquid is the temperature at which its vapor pressure equals the external or atmospheric pressure. At this temperature, every molecules of the liquid acquire enough kinetic energy to overcome the intermolecular forces attracting them to the other molecules. Therefore, boiling points
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These bonds occurs when a hydrogen atom is bonded to oxygen, nitrogen, and fluorine atom of another molecule, or when a hydrogen atom is electrostatically attracted to a lone pair of electrons on oxygen, nitrogen, or fluorine atom of another molecule.Therefore this essay aims at exploring the relationships between the literature boiling points of four organic compounds (1-Pentanol, 3-Methyl-1-Butanol, 2-Hexanone, and 2-Pentanone) using the background theory of the various factors that affect the intermolecular forces within molecules of varying boiling …show more content…
From proceedingdiscussion, one might expect that both compounds should have the same boiling points because of their similar molecular weight (88.2amu) and since both alcohols contain hydrogen directly bonded to oxygen, and therefore each molecule possess hydrogen bonding as additional intermolecular forces. However, this is not so because the differences in boiling points between these two compounds cannot clearly be attributed to the molecular weight and hydrogen bonding alone. The key to understanding these trends is to realize that although both compounds have similar molecular weight, but they also have different molecular shape and size (surface area). The larger and elongated shape of 1-pentanol provides a greater surface area available for contact between molecules, resulting in corresponding increase in the strength of dispersion forces between them, thus higher boiling points. In contrast, the smaller and more branched, spherical compact shape of 3-methyl-1-butanol offers a smaller surface area available for intermolecular contact which lowers the strength of the dispersion forces, resulting in corresponding decrease in boiling points observed. Thus, the order of boiling points between the two compounds is: 1-pentanol >

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