With the (relatively) warm weather here, it’s a good time to look at sunscreen chemicals! Avobenzene (IUPAC name 1-(4-Methoxyphenyl)-3-(4-tert-butylphenyl)propane-1,3-dione) is a popular ingredient of sunscreens. It is part of the “Helioplex” sunscreen system marketed by Neutrogena. Like almost all sunscreen compounds, it contains benzene rings, since these are good at absorbing UV light. In the case of avobenzene, it absorbs a wider range of UV light than many other similar chemicals and so is well-suited for its purpose of shielding us from the sun. One deficit of avobenzene is that it tends to break down rather rapidly under UV light, so it is normally packaged together with another chemical to help it stay stable. In the case of Helioplex, the compound oxybenzone is used.