I want to record this short video to show you a little bit more about how to determine RS and use your hands to be able to determine which direction those groups are going to go. I have three examples on the board with four different configuration, with four different stereogenic carbons that we want to take a look at in this regard. So let's take a look at the molecule here on the upper right first. If you take a look at this, what we have is a stereogenic carbon right here that we need to determine the RS configuration for. And you notice there's three bonds that carbon, so one is missing and that would be a hydrogen and it's useful to draw in that hydrogen so you know which direction is going. So these two bonds are in the plane of the board, whereas this bond is coming out towards it. So that means the hydrogen that's not drawn here must be going to the back. So I'll just put it back here to the back. And now what we have to do is determine what the configuration is by assigning the priorities. So if you need some help, go back in and review how to assign your priorities, but I'll do it rather quickly here. This carbon that's attached to oxygen would have priority number one. This carbon which is attached to other carbons and double bonds is going to be priority number two. This carbon will be priority number three and of course the hydrogen will be priority number four. Now this is an easy example because the hydrogen is pointing away from us and from that viewpoint remember if you go from one to two to three in this case in a counterclockwise direction that would be the ask configuration. If it were to go in the clockwise direction it would be our configuration. Now how do you do that with your hands? How do you figure that out with your hands? Well if you imagine your thumbs as being the lowest-party group hydrogen, it's not pointing towards us, it's pointing away from us. So if you stick that directly into the board in the direction of that hydrogen, if you go from one to two to three you need your left hand to curve in that direction. So thumb to the back, left hand curves from one to two to three, so left hand would be the ask configuration. Okay? Let's take a look at this one also. I'm going to draw in the hydrogens that are not shown here. So in this case there would be a hydrogen going back from that carbon and there would be a hydrogen coming towards us from that carbon. So let's take a look at this configuration first. So let's assign the priorities to the groups. In this case the oxygen is going to have highest priority. Next if you go this way around the ring you get to a branch closer than if you go this way around the ring. So this is second priority, this would be third priority and of course the hydrogen would be the fourth priority. So in this case going from one to two to three is going in a counterclockwise direction but the hydrogen is coming towards us. If you can envision it in your head looking at that from the backside and know that that's going to the right it would be the arc of configuration. But if you need to use your hands to do that the hydrogen is coming up, you point your hands directly towards your face and so in order to go from one to two to three you need your right hand to curve in the direction of the order of one to two to three. Okay? Your left hand would be going in the opposite direction. I was hydrogen is coming up, point it directly at you off of the plane of the board or the plane of the paper. Okay, where the hand situation can come in useful is when we have a situation like this. Notice what I've done here. I'm drawing this molecule where the priority groups are one, two, three and four. Notice the lowest priority group hydrogen is in the plane of the paper. It's not coming towards us or going away and that can be a little bit confusing. If you can envision your eyeball here looking down in this direction you could see that you need to go from bromine to the carb two to three in this direction. But sometimes it's hard for you to manipulate that in your head and view that three-dimensional group. With your hands it's easy. So if it's in the directly in the plane of the board you need your right hand pointed this way or your left hand pointed directly that way and we have the hydrogen. So if you go from one to two to three you need your left hand to go from bromine to carbon and then towards you. If you use your right hand you're going from bromine to what's coming towards you first. So it's the left hand pointed in the direction of the hydrogen that you need to do this. So that would be the S configuration. Again if you can look at it from this direction what you'd see is bromine, that group, CH3 and the hydrogen going directly back you'd see that that's the S configuration. So look carefully at the three-dimensionalality of the molecule. If you can do that in your head otherwise figure out where your lowest priority group is point your thumbs in that direction. If it's coming up, point of straight up, it's going away, point straight down. If it's in the plane, point it in the direction it is on the plane of the paper and see which way you need to use your hands. In this case bromine starts in the back to here to the forward so you need your left hand. I hope that helps explain how I use my hands to determine the R and S configurations.