Substitution reactions can have really powerful effects, both good and bad, in our bodies. You might remember substitution reactions as displacement reactions from general chemistry, but (you guessed it!) in organic chemistry they’re a bit more complicated. In this episode of Crash Course Organic Chemistry, we’ll learn about the two pathways substitution reactions can take: SN1 and SN2 mechanisms, which substrates prefer which mechanism, and we’ll apply this knowledge by looking at how substitution reactions make chemotherapy treatments work.