Organic Structures - Organic Chemistry Concepts: An EFL Approach - page 9

FIGURE 1.8
Induced-dipole/induced-dipole intermolecular forces.
Generally, as molecular size increases, so does the total van der Waals interac-
tion. The efficiency of this attraction can also depend on molecular shape, and
how well the molecules can fit together. Therefore, as chain-branching increases,
the efficiency of the van der Waals interaction between molecules decreases as
shown in Figure 1.9 .
FIGURE 1.9
The dependence of intermolecular forces on size and shape.
The polarity and type of intermolecular interactions of organic molecules can
also explain their solubility properties. Organic compounds generally have low
solubility in polar solvents like water. This is because they are either non-polar or
only moderate polar. This means they have little attractive interaction with the
solvent molecules. In contrast, ionic compounds can ionize and polar solvent
molecules can interact strongly with the ions. This interaction, called solvation ,
makes the ion more stable and helps with solubility.