The hydrogen bonds that hold together the molecular base pairs of our DNA form in intracellular fluid. Much of our planet's environmental chemistry occurs in oceans and other bodies of water. Most drugs are synthesized in solvents. Yet chemists generally study the bond-by-bond mechanics of chemical reactions only in the gas phase, where molecules are relatively sparse and easy to track. In a liquid there are more molecules and more collisions among them, so reactions are fast, messy and complicated. The process you want to observe will look like an undifferentiated blur—unless, that is, you can take snapshots of the reaction in a few trillionths of a second.