Benzophenone is not soluble in water because it is nonpolar and water is polar. The polarity of any two chemicals is one of the most important factors when determining solubility or insolubility. In this regard, benzophenone and water are incompatible and thus insoluble.
Solubility is the ability of a chemical to dissolve when reacting inside another substance. Solubility is very closely tied to polarity. In chemistry a substance that is polar has an imbalance of electron density. In other words, it has multiple different physical characteristics at different points along its structure. Water molecules are polar because they are formed in a way that results in one partially negative end and one partially positive end. For a chemical to be soluble in water, it must be able to bind to the water molecules. However, benzophenone molecules are structured in such a way that they have the same physical reactions to other chemicals at all points on their molecular structures. Because water is polar and benzophenone is nonpolar, they do not cause the prerequisite reactions in one another for solubility. Benzophenone molecules cannot bind to water molecules and do not dissolve. However, benzophenone is soluble in other polar substances to which it can bond.