Functional groups are important building blocks for future study. You don't "have to" memorize them, you "get to." Since it is now your attitude that it is an honor and privilege to memorize stuff, let's get it done faster and easier. Use Harry Lorayne's memory system for numbers and you have it made.
Note: I am letting you know my personal yet somewhat inappropriate memory tricks. Many of them were offensive to me, or simply made me laugh. You don't have to, and should not, share your tricks with others. I have to, or rather, I get to, so you learn from my experience.