Now we're going to say here, we recently learned that a Cairo molecule is basically a molecule that contains a carbon that is connected to four different things. Now we're gonna say, one key feature of Cairo molecules is that they rotate plane polarized light. So what we need to realize here is that we have a light source or light bulb or a flashlight, anything that can emit light. And what normally happens with regular light is that it oscillates basically the light goes in all directions and then what's the effect of this? If we were to shine that light through some type of solution, the light would go through the solution. Now, the special thing about Cairo centers is if we have a solution made up of a Cairo molecule, it will actually bend the light. The light will actually bend to the left or to the right, it won't shine through the solution. And in order for us to determine how much to the left or to the right that it bends, we use what's called a pola rahm iter. So basically this is the apparatus for pola rahm iter. And what the pope paul Romer measures is your observed rotation alpha. This basically tells me, does it band 60° to the left, which will be negative 60° or does it bend 60° to the right, which will be a positive 60°. Now we have terms that are associated with this bending of light. So here, what we have is two solutions and both of them have a flashlight shining on them. Now here, if we say the solution, we shine the light on it. Let's say it bends like clockwise when it bends like clockwise. That means it's bending light to the right. So if it bends light to the right, it's known as dextre literate story or lower case. D if it's bending like to the right, it has a positive observed rotation. So let's say that this is a positive six degrees that I said earlier. Now here let's say we have another solution and this solution, we also basically shine a light on it. But let's say it bends the light counterclockwise, which means left here. Since it bends light to the left, it's known as live oratory oratory Here, it's bending light to the left. So I would have a negative observed rotation. So let's say that this is negative 60°. Now we're going to say that these two solutions have basically the same degree 60. And the only thing that's different about them is which direction does it point in terms of degrees, we're gonna say to Cairo solutions that point light in completely opposite directions are financial MERS. So these two solutions represent an anti american solutions. One Cairo compound and its exact mirror image in the other solution, they've been light in completely opposite directions. And in fact this is one of the key differences between an tumors in an tumors have the same boiling point, same melting point, same density, same formula, same. Mass same connections. The only things that are different about them are their configurations which you're not gonna learn hearing, you're gonna learn that inorganic and their observed rotation. So we only have two things that are different about them. Their configurations and the direction bend light either to the left or to the right. Now. Hear the names and degrees of rotation have nothing to do with the chirality of compounds, let's say you were able to determine the configuration of one Cairo center and in that example it bent line to the right. But you could take a completely different coral center. It could have the same exact configuration as the one you just looked at. But it's observed rotation could be in the opposite direction when you guys get to again, if you are in greater detail, how can we exactly determine which direction is the Cairo solution? Bend light. And you'll learn about different formulas that are involved with the polaroid emitter. But for right now, the key thing you need to realize from this is a Cairo compound can bend light to the left or to the right. If it bends light to the right, it's called dextrose oratory, which is lower case. D if you're bending light to the to the right, it's called the clockwise direction or clockwise rotation and it has a positive observed rotation if you've been light to the left. You're known as leverage oratory or lower case. L have you been light to the left? You're counterclockwise in terms of rotation, which would mean you have a negative observed degree now that we know that and now that we know that Cairo centers create optical activity. I want you guys to answer. The following question I asked which of the foreign compounds would be optically active. So it deals with what we just talked about. So I'll give you guys some time to do this. Come back and take a look on how exactly do I approach this problem and how best to answer it?