When the reaction of two compounds results in a product that contains all the mass
of the two compounds, the product is called an addition compound. There are several
kinds. In the rest of this chapter, we will discuss addition compounds in which
the molecules of the starting materials remain more or less intact and weak bonds
hold two or more molecules together. We can divide them into four broad classes:
electron donor–acceptor complexes, complexes formed by crown ethers and similar
compounds, inclusion compounds, and catenanes.