Quantitative Structure-Property Relationships of Cycloalkanes
By Charles Xie ✉
Cycloalkanes are a family of hydrocarbon molecules whose carbon atoms form a single ring (i.e., monocyclic). Like the linear alkanes, their boiling points also increase with the number of carbon atoms. With AIMS, you can study this quantitative structure-property relationship (QSPR).
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Aside from cycloalkanes, other hydrocarbons such as linear alkanes and acenes also observe this relationship.
QSPR modeling gives us a tool to analyze the data, but it does not provide any explanation about the result by itself. To make sense of the result, we still need to resort to fundamentals in chemistry. Equipped with the power of molecular dynamics simulations, AIMS allows us to design and conduct computational experiments to check a QSPR model.
Molecular Dynamics Simulations
The following two simulations allow you to compare the boiling points of cyclopropanes and cyclodecanes on a qualitative basis.
Cyclopropanes (C3H6)
There are 22 cyclopropane molecules (198 atoms in total) in this simulation. The temperature is initially set to be 300K (27°C or 80°F). A greatly exaggerated gravitational field is applied to keep the molecules at the bottom of the container when they condense. As you can see, at this temperature, these cyclopropanes are in a gaseous state.
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Cyclodecanes (C10H20)
There are seven cyclodecane molecules (210 atoms in total) in this simulation. The temperature is initially set to be 300K (27°C or 80°F). As is in the case of the cyclopropanes above, a greatly exaggerated gravitational field is applied to keep the molecules near the bottom of the container when they condense. As you can see, at this temperature, these cyclodecanes are in a condensed state occupying the lower part of the container.
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While the boiling points of cyclopropanes and cyclodecanes predicted by our molecular dynamics simulations may not agree exactly with the experimental data (-33°C and 201°C, respectively), it is clear that the simulations show that cyclodecanes have a higher boiling point than cyclopropanes. The higher boiling point of cyclodecanes may originate from the fact that they have more intermolecular interactions to hold them together, as indicated by the dashed lines shown in the above windows.