My professor was saying something about cycling, how it compacts the structure, and how it relates to solubility somehow. He used the example of cyclohexane vs. hexane, but I didn't catch what he said. And then he mentioned proline, which is a cyclic amino acid. Did he mean that cycling will make the molecule more soluble in water?
Cycling, or the formation of cyclic structures, can indeed have an impact on the physical properties of molecules, including their solubility. Let's take a closer look at the examples your professor mentioned and explain how these concepts relate.
First, let's compare cyclohexane and hexane. Hexane (C6H14) is a straight-chain alkane, while cyclohexane (C6H12) is a cyclic compound. The cyclic nature of cyclohexane allows its carbon atoms to adopt a more compact, "puckered" structure, as opposed to the straight, extended structure of hexane. This compact structure significantly reduces the molecule's overall surface area, which affects its interactions with other molecules, including solvents.
In the case of cyclohexane, its compact structure decreases the number of potential exposed hydrophobic (water-repelling) sites, making it less able to interact with water molecules. As a result, cyclohexane is not very soluble in water. In contrast, hexane has a larger surface area due to its extended structure, making it more able to interact with water molecules. Therefore, hexane is more soluble in water than cyclohexane.
Now, let's discuss proline, which is an amino acid with a cyclic structure. The cyclic nature of proline allows the formation of a secondary amine and creates a five-membered ring structure. This unique structure plays a role in the properties of proline, including its solubility. The cyclization of proline changes its chemical properties and makes it less polar compared to other amino acids. As a result, proline is less soluble in water than amino acids without a cyclic structure.
To summarize, in general, the cyclization of molecules can result in a more compact structure, which can affect the solubility in water. Reduced surface area and altered chemical properties due to cyclization can lead to decreased solubility, as is the case with cyclohexane and proline. However, it's essential to consider the specific molecular structure and the interactions involved to determine the exact impact on solubility in any given scenario.