Why does shielding in organic molecules cause lower solubility in water?

The phenomenon of shielding in organic molecules causing lower solubility in water can be explained by considering the nature of these molecules and the interactions they have with water.

To understand this phenomenon, we first need to know that organic molecules generally consist of carbon and hydrogen atoms, sometimes with other atoms like oxygen, nitrogen, or sulfur. Water, on the other hand, is a polar molecule, meaning it has regions of partial positive charge (hydrogen atoms) and partial negative charge (oxygen atom).

When we talk about shielding in organic molecules, we are referring to the presence of nonpolar groups, such as hydrocarbon chains or aromatic rings, which are electron-dense and can create a barrier or shield around the polar functional groups of the molecule.

Now, water molecules interact with solutes through intermolecular forces, specifically hydrogen bonding. In order for a molecule to be soluble in water, it needs to be able to form favorable interactions with water molecules.

In an organic molecule, if nonpolar shielding groups (hydrocarbon chains or aromatic rings) are present, they create a hydrophobic, or water-repelling, environment around the polar functional groups. This is because water molecules, being polar, tend to avoid nonpolar areas.

As a result, the water molecule-water molecule hydrogen bonding is disrupted in the presence of these nonpolar groups, making it energetically unfavorable for the organic molecule to dissolve in water. The shielding prevents the water molecules from effectively interacting with the polar groups of the organic molecule, leading to lower solubility.

In summary, shielding in organic molecules, caused by the presence of nonpolar groups, reduces their solubility in water by creating a hydrophobic environment that disrupts the favorable interactions between water molecules and the polar functional groups of the organic molecule.