A solvent is a chemical that can react with other chemicals to form weak bonds that suspend both chemicals in a stable form. For a chemical to be a good solvent, it must be able to surround the dissolving chemical and prevent separation of the two substances while temperature and pressure are maintained. Not all solvents work with all chemicals, so the correct solvent must be chosen.
How Solvents Work
Solvents dissolve other chemicals into a solution in which the solvent chemically bonds to the dissolved compound. Molecules in the solvent position themselves around the individual molecules from the dissolved substance, forming a compound that is more thermodynamically stable and, therefore, less reactive under standard conditions than the solvent and dissolved chemical on their own.
The Composition of Xylene
Xylene, also known as dimethylbenzene, is an organic molecule that exists in three forms, known as isomers: ortho-, meta- and para-xylene. The isomers refer to the positions of the methyl groups (composed of a carbon and two hydrogen atoms) on the benzene ring at the center of the xylene molecule. It is this structure that makes xylene a good solvent.
A dipole moment is the strength of the magnetic field created by a molecule with an unbalanced distribution of electrons in its covalent bonding structure. Because xylene possesses a benzene ring structure, which requires the sharing of an electron between the six carbon atoms in the structure, it contains a large dipole. As the molecule is polarized, it is able to bond tightly with other polarized molecules and act as a solvent.
Hydrogen bonding occurs when a chemical with a small dipole moment is attracted to the magnetic charge on another weakly polarized chemical. With xylene, the effect of the benzene ring's electron-sharing covalent bonding means other electrons within the molecule's bonds are attracted toward the ring structure, which causes weak polarization. This allows the molecule to exert hydrogen bonds and act as a solvent in a similar method to how water dissolves other chemicals.
Again, the structure of xylene is such that it creates an unstable distribution of electrons and thus can be easily polarized by the presence of strongly, or even some weakly, polarized molecules, and also affect polarization in other molecules. The result of this polarization is that the two molecules can form bonds with one another via Van der Waal's force. The effect is that the polarizing chemical is surrounded and dissolution occurs.