Relationship Between Structure and Boiling Point: Organic Compounds

This discussion post delves into the relationship between the boiling points of chemical compounds and their structural characteristics. It explains that boiling point is the temperature at which a liquid's vapor pressure equals the surrounding pressure, leading to a phase change from liquid to vapor due to the breaking of intermolecular bonds. The discussion focuses on two organic compounds: 3-methyl-2-butanone and 1-pentanol, with boiling points of approximately 94-95°C and 137°C, respectively. The higher boiling point of 1-pentanol is attributed to the presence of strong hydrogen bonds, while 3-methyl-2-butanone exhibits lower intermolecular dipole-dipole forces due to its methyl groups and altered carbon backbone. The post references PubChem and includes structural diagrams to illustrate the chemical bond arrangements and their impact on boiling points, along with the molecular weights and chemical names of the compounds and relevant references.

Discussion to relate the Boiling point with the structural factors of the chemical compounds:
Boiling point is actually the temperature point at which the vapour pressure of the liquid will
become equal to the pressure surrounding the liquid. This is at this temperature, the liquid will
change its phase to the vapour. At microscopic level at BP the intermolecular bonds will break and
the vapour phase changes do occur. Hence higher the bond energies, higher BPs will be required to
break the bonds and for changes the phase from liquid to vapour.
In the current scenario the two chemical compounds selected for the study are both organic
compounds. One of the two is 3-methly-2 butanone and the second compound in the list is 1-
pentanol. The boiling point of the first element 3-methyl-2 butanone is about 940C to 950C and the
boiling point of the second compound 1-pentanol is around 1370C. Intermolecular forces in the
chemical compounds do directly depend on the type of the bonds present in the chemical
compound and they will immediately impact the extent of the forces needed for breaking the
chemical bonds. Hence in this connection it can be said that the boiling point of the compounds will
be higher for the compounds requiring higher forces to break the bonds and the boiling point of the
chemical compounds will be lower for those compounds which require lesser bond breaking forces.
In this connection the relative differences of the boiling points of the two chemical compounds is
explained in the following discussion. The BP of the 1-pentanol is higher than the BP of the 3-methyl-
2 butanone and the reason for the same can be explained due to the chemical bonds present in the
respective chemical compounds. 1- Pentanol mainly consist of the hydrogen bonding. Hydrogen
bonding is responsible for the strength of the 1-pentanol. 3-Methyl- 2 butanone chemical
compounds intermolecular bonding is distinct from that of the 1-Pentanol. In this chemical
compound there is presence of the methyl groups and the presence of the same will result in the
change in the carbon backbone bonds. There will be four carbon backbone with a single carbon
branch on the third carbon atom. And so this will result in the decrease in the intermolecular dipole-
dipole bonds, so this feature will result in the lower Boiling point of the compound. Hydrogen bond
of the 1-pentanol is stronger and hence is responsible for the higher boiling point of the compound
when compared with the 3-methyl-2 butanone chemical compound (PubChem).
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The above figures provides the details and the arrangement of the chemical bonds present in the
molecule and they in turn explains the strength and the boiling point of the chemicals.
Chemical compound details
3-Methyl-2-butanone
Chemical names:;iso-
C3H7COCH3;Methylbutanone;3-
Methyl-2-but;2-Acetylpropane;2-
Acetopropane ;3-
Methylbutanone;3-
Ketoisopentane;Methyl
butanone-2;Methyl-2-butanone
Molecular weight of 3-Methyl-2-butanone = 86.13gm/mol
1- Pentanol
Chemical Names:
1-Pentanol; Pentan-1-ol; Amyl alcohol; N-Pentanol; N-Amyl alcohol;
Pentanol
Molecular weight of Pentanol =88.15g/mol
References:
Etter, M.C., 1991. Hydrogen bonds as design elements in organic chemistry. The Journal of Physical
Chemistry, 95(12), pp.4601-4610.
Giese, B. and Baldwin, J.E., 1986. Radicals in organic synthesis: formation of carbon-carbon
bonds (p. 141). Oxford: Pergamon Press.
Anon., n.d. [Online]
Available at: https://pubchem.ncbi.nlm.nih.gov/compound/3-methyl-2-butanone#section=Top
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Anon., n.d. [Online]
Available at: https://pubchem.ncbi.nlm.nih.gov/compound/1-Pentanol
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