Tetraline (More less explodey hydrogen)

As I've mentioned in the past, chemists often need to reduce a molecule by adding hydrogen. A medicinal chemist might get to an azide by way of an amine, or a food chemist might want to get to a saturated fat (or, although it's less and less popular, a trans fat).

Adding hydrogen can be done with a catalyst and, well, just hydrogen gas. It's a gas and flammable under a huge range of concentrations. Even gasoline only burns in a narrow range in air - don't go sticking a lit stick in your gas tank, but it would just snuff it out. This is why molotov cocktails work. The gas-soaked rag will burn, but it'll just snuff out unless it's thrown and shatters, allowing the fuel to vaporize and start on fire.

Hydrogen, however, doesn't take much oxygen to take off. For this and other reasons, "transfer hydrogenation" from something that's happy to give up a few hydrogens works well. Previously I mentioned cyclohexadiene, which happily gives up its hydrogens in order to become benzene, a molecule that's energetically downhill because it's aromatic.

Upon undergoing transfer hydrogenation, tetraline goes to an even larger, lower-energy aromatic system - naphthalene.