Now I want to briefly touch on another form of nuclear magnetic resonance. Except this type of NMR is going to detect carbon 13 isotopes instead of protons. And this is fittingly called carbon 13 and, um, are carbon 13. NMR is a more limited type of nuclear magnetic resonance. In contrast to Proton NMR, there's actually less information that we can get from carbon 13 than we can from Proton NMR. And this is largely in part to the low natural incidence of the carbon 13 isotope. I'm not sure if you guys recall from Gen. Cam, but if you guys remember, Carbon 13 has a natural abundance of about one out of every 100 carbon atoms will be a carbon 13. Okay, So because there's so few carbon 13 in this, you know, in molecules, that means that splitting remember, one of the major forms of information that we get in proton NMR is not observed at fault. Okay, you do not get any splitting in carbon 13 and, um are. And if you do the math, that makes sense, because if you think about it, the only way splitting could occur is if you have a carbon 13. That's next to another car with 13 so they can interfere with each other, Right? But if the natural incidence of carbon 13 is one in that means that the chances of getting to carbon 13 next to each other are one in 100 times two. So that means that the chances that you would actually get these two carbons to split each other is actually 1/10 1000. Okay, so the math just gets too crazy. Um, it's such a It's such a small percentage of our carbon 13 that will split that we just basically say that is not observed it all. Okay. Other than that, we're going to see all of the major themes that we learned in Proton NMR carried over into carbon 13 NMR. The only difference is being we're not detecting hydrogen is anymore. We're detecting carbons. We're not getting any splitting, and we are gonna have to learn some new shift values in our in terms of our chemical shifts because the instrument is calibrated differently. Okay, Now what? You're gonna notice that the same general pattern applies if you were just to not look at these numbers. And just look at the order of these of these groups. You see that? They're all in the same exact order. We have Al cane. We have alkaline. We have our Electra negatives. We have our Al Keen. We have benzene, we have carbon eels. So really, the order hasn't changed at all. It's just the absolute values that have changed because the spectrum of ah of a carbon 13 NMR goes from about zero to about 210. So it's just a different set of values. Okay, now, to make things a little bit better for you, just the fact that, like these values, didn't really change a lot helps. But also it's extremely rare for professors to ask you to memorize these values because they tend to not care as much about carbon 13 because just not as not as helpful of a analytical methods. So many times, they'll tell you that you don't really need to know these shift values. You should just be familiar with them. So in that sense, if you're familiar with Proton NMR, you're already familiar with carbon 13 NMR in terms of the ranges and in terms of the order of the different types of of ships. Okay, so we're gonna go straight into some practice problems that kind of help us to solidify our knowledge of carbon 13 NMR. I want you to go ahead and answer this question, and then I will go ahead and answer it for you. So take a shot at
Identifying 13C Signals
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All right, So how many different signals did we get? Well, this is definitely going to depend on whether you saw symmetry or not. And actually, it turns out that there is symmetry in this molecule because we've got the benzene ring that's exactly the same on both sides. And we actually have symmetry along this bond. Now, you might be wondering, maybe you're under the impression that there wasn't any symmetry because you see this CH three that's kind of off tilted to one side. So you're thinking that, you know, this is an asymmetrical molecule, But again, guys remember single bonds can rotate as much as they want. So really, even though it's drawn that way right now, remember that this CH three could easily go to the top. Could easily go to the side. It could easily rotate all around there. So actually, there's a perfect plane of access all the way through this molecule. Just imagine that the stage three rotated, so it's right underneath that dotted line. Sorry. I know that was tricky, but it's stuff you have toe be able to visualize. So now recall we're not concerned about hydrogen is here just different types of carbons. So that means that every carbon gets a peek, a signal, even the ones without hydrogen. So this is gonna be my first type. This is gonna be signal A this hoops different color. This is going to be signal. Be as well as this one over here. This is gonna be signals. See, along with this one over here. Now, this is where things change a little bit from proton NMR. This one gets its own signal. That signal D Okay, this one is Signal E. And then finally, we have signal f. Okay, so this one would have six signals. Okay. So many times what we'll see with carbon 13 and, um are is that you get a different number of signals than you would just proton NMR because you have different. You know, you're looking for a different type of Adam. Okay, Awesome. So now let's move on to the next question. Just look at all four compounds and try to see which compounds would, you know, meet these criteria of only having one peak for both the proton NMR and the carbon 13 NMR. So go ahead and then we'll just answer all four once
1H and 13C Joint Problem
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and the answer is Onley Compounds be and C will yield one signal each for proton, NMR and carbon 13 NMR. If we look at compound a compound a wood on Lee, give us one signal for proton NMR. Okay, that would be the signal. That's experience right at the end. However, we would actually get to separate signals. Four carbon 13 do upsets will be a carbon two signals, so that one was out. Now we look at D D is kind of in the same boat where we would get one signal for Proton NMR, but we would get to signals for carbon 13. So these questions obviously do not work. Okay, These those answers do not work. Okay, so that was just a quick overview of carbon 13 and, um, are let's go ahead and move on to the next topic.