Things have been getting more and more complicated here in Crash Course Organic Chemistry, and as we deal with more complex molecules, parts of molecules we don’t want to react will start reacting along with the parts that we do. Luckily, we have protecting groups, which act like a chemical disguise and help us control how molecules react. In this episode, we’ll look at what makes a good protecting group, as well as identify some good protecting groups for different functional groups. We’ll also see what role protecting groups play in the synthesis of penicillin!