hopefully you find the ted talk to be kind of entertaining because they're much higher production than my videos um in any case that video is useful because it set us up to understand what is chirality and and we're going to focus on that in just a bit but i do want to show before i go on to the details just kind of the hierarchy of the different isomers and what is an isomer in the first place before we go on to the details so here's kind of the hierarchy how do you know if something is an isomer versus not an isomer now as long as molecules have the same molecular formula they're going to be considered isomers from one another so for example there's a whole different ways that you can draw the molecule c4h10o o but that molecule is not going to be an isomer to c2h6 because they don't have the same number of uh carbon hydrogen oxygen and so on right so they're not the same number of stock so that that's what it means by an isomer versus not an isomer um if it's not an isomer it's simply because their molecular formula is entirely different all right so that's kind of the first hierarchy so what is an isomer in the first place now there's a we separate it again by constitutional isomer versus stereoisomer we are actually not interested in this one because constitutional isomer simply means that the molecules are different they're different molecules so for example i can have molecules of c4h10o that would look something like this versus the same molecule or same molecular formula that looks like that right so the oxygen here is located in different locations so these are examples of constitutional isomer i can even have something that looks like that so these are all combinations of constitutional isomers they're basically different molecules we're not interested in those because different functional groups different naming and so on or the name is different enough that we're not too interested it's just different molecules now what happens is that now we have classes of molecules that's called stereoisomers and for example if we have a molecule that look like this versus a molecule that look like this right there's still c4h10o but these two now are considered stereoisomer their structure is the same and so on and so forth but um but notice here the o h here on one on the one on the left is sticking out of the board whereas the o h on the uh the one on the right is sticking into the board right so that's going to be example of a stereoisomer now we're going to break it down even more now sometimes there's going to be what's called a configurational isomer and essentially these ones uh cannot rotate right so so there's a lot of different ways that you can have an isomerism and there's a conformational and there's going to be configuration a confirmation one is not interesting to us either because it simply means that it's the same molecule but if your molecules kind of bump around and rotate and so on they will become the same molecule again so for example these two molecules here for the cyclohexanes are exactly the same formula but you can see that you know it this one looks like a boat this one looks like a chair so what happens is that they're not technically the same structure they're just the confirmation is slightly different but what happens is that um the molecules the single bond could rotate so what happens is that it kind of the molecules would bounce around between these two states from one to the next to next to the next over time now of course the there's going to be some probability for uh in terms of their distribution for example this one is slightly more stable compared to that one so maybe you have for example 80 percent look like this at any given moment in time and 20 looks like that at any given moment in time i'm pulling numbers randomly here but the the point is that the molecules would interchange between one to the other just like in equilibrium um but the reason why some scientists might be interested in conformational isomer is that well maybe the chemical reaction will only occur when the reaction when the conformation looked like this versus that so that would change the rate of reaction so for example the rate of reaction of this particular molecule might be slightly different than that now that you have a composition of both at given moment in temperature how do you then sort out and and write down the proper rate of reaction that's just an example but in actuality the same the molecules the same molecule they were interconvert from one to the other so in the grand scheme of things we are not yet interested in this because we're just an intro class and the details of that would be quite a lot so we're not going to go in there as well uh what we're interested in is the configurational that is no matter what you do you can't rotate them or anything to make it look like one another and then we have now essentially a difference between a cis trans configuration cis and trans configuration or geometric isomers or optical isomers and that's going to be where the chiral comes in so what's the difference between the system trans and the optical one now the cis and trends geometry would involve double bonds or cyclic right alkanes in this case so for example because the double bond could not rotate right you cannot interconvert from one to the other so this into conversion from one to the other does not happen and therefore they're going to be two different molecules and the same with this for example this one here is sticking into the board and this one is sticking out there's no possible rotation that could happen they would allow this particular transition and therefore they're going to have a system trans um classification and we will go into details later so we're going to be interested in this one now the one on the video that you watch about kind of isomers and ends and chirals and so on are essentially called the optical isomers or i'm just going to call them chiral there's going to be two different kinds of distinction between the aster the asterismers versus enantiomers we're not going to go into that just yet i will leave that for the next class to go what i wanted to be able to do is identify whether it's cis and trans and whether they have a chiral centers and so on so that's going to be the scope that we're going to cover in the class