 Okay, so this one again should be reviewed from last semester, but I think it's a good one to go over really quick. So we can think of these two reactions. So and ask ourselves, we'll compare them, and ask ourselves which one would you think would be the faster SN1 reaction? Would it be the top one here or the bottom one here? Yeah, and you guys are already saying of course the bottom one, right? You remember from last semester why, right? It's because of course both the fluorine and the bromine. I guess so let's start and say, well what is an SN1 reaction, right? What's going to happen, this is polar solvent, so that's going to lose the leaving group because we've got a secondary alkyl halide and the mechanism of course would be very similar for this one, it's just the F instead of the Br. And what we would make effectively is the secondary carbocation. So that intermediate there and it's going to be the same intermediate, well let's draw it over here. For both of these ions or for both of these reactions, so that's secondary carbocation. So since you have the same solvent, make the same secondary carbocation, the only determining factor, the rate determining factor should be what is the leaving group. So that's what we're really looking at, which is the better leaving group. So that's the real question we're asking here when we're really asking which is the faster SN1 reaction. So which is the better leaving group? Well, they both have a negative one charge. So that's what you're really looking at as, well you've got to compare their charges. It's the same charge so now we've got to compare something else. Well, we've got to think, well the fluorine is very small relative to this huge bromine. And since they have the same charge, negative one, right, but the bromine has a much bigger surface area and they don't like to have that charge concentrated so what they'll try to do is kind of push it around their surface area like that. But since you've got more surface area on the sphere of this huge bromine, and think of these as all partials, if you will. So since it's the same negative one charge, you've got a very big surface area to spread it out, this actually is more stable, the bromine anion is more stable by itself than the fluorine is. So the fluorine actually wants to stick very close to the alkyl portion of this alkyl halide. So the bromine doesn't mind so much to have that negative charge because it's very big and it can distribute it around its surface area and the fluorine can't do it as well. So that's really what you're looking at is the size of the leaving group. So since the size of the leaving group is much bigger and bromine, it's going to be the faster SN1 reaction. So let's just finish it off, just write that. Which one's the faster? Bromine is faster, the fluorine is slower. Makes sense, right? Okay, cool.