Why are alkyl halides insoluble in water?

Alkyl halides, which are compounds containing a halogen atom (such as fluorine, chlorine, bromine, or iodine) bonded to a carbon atom in an alkyl group, are typically insoluble in water due to differences in polarity.

Water is a highly polar molecule due to its bent shape and the unequal sharing of electrons between oxygen and hydrogen atoms, resulting in partial positive and negative charges (a dipole). Alkyl halides, on the other hand, are often nonpolar or only slightly polar, depending on the size of the alkyl group and the nature of the halogen atom.

The carbon-halogen bond in alkyl halides is polarized, with the halogen being more electronegative than carbon. However, the presence of the alkyl group can diminish the overall polarity of the molecule, particularly if the alkyl group is large.

Because water molecules are more attracted to each other through hydrogen bonding and dipole-dipole interactions, they tend to exclude nonpolar molecules like alkyl halides. The weak dispersion forces or induced dipole-induced dipole interactions between water and alkyl halides are typically insufficient to overcome the strong cohesive forces within water, resulting in poor solubility of alkyl halides in water.

Instead, alkyl halides tend to dissolve better in nonpolar solvents such as diethyl ether, chloroform, or carbon tetrachloride, where the intermolecular forces are more compatible with the alkyl halide molecules.