So how many neighbors? One, two, three, so three Protons do we have? Well, those protons in blueĪre attached to this carbon. So, over here, thisĬarbon has two protons, so we expect one signal for those protons, and then over here, thisĬarbon has three protons, so we would expect another Alright, let's look at another example for a coupling constant, so let's look at this molecule, and let's focus on the ethyl group. Which it is coupled, sometimes it can help you when you're trying to understand what's going on in your NMR spectrum. That they're pointing towards the proton with This on an NMR spectrum, and if you think about Where you get these doublets with like a roof over their head. Points toward the proton with which IT is coupled, and so you get this situation Towards the higher peak, and so the doublet So this peak's a little bit higher, so we draw an arrow pointing
So the doublet points towards the proton with which it is coupled, and the same thing for this signal. Signal for the red proton, which is causing the So that arrow is pointing to the right, and that's where we find the Pointing towards the higher peak, that arrow points towards the signal of the proton that'sĬausing the splitting. Is a little bit higher, and if you draw an arrow Two peaks were the same, but if I look at the actual NMR spectrum, they're not quite the same. Spectrum with interaction, the spectrum with couplingīetween the protons, we just assumed that the heights of these Proton is right here, and the signal for theīlue proton is over here. The actual NMR spectrums, over here is a zoom-in of The reason why we use Hertz, is because it's the same coupling constant no matter what NMR spectrometer you're using, so it doesn't matter what Is measured in Hertz, so it turns out to be 1.4 Hz, and if it's 1.4 Hz for this one, it must be 1.4 Hz for this one, because those protonsĪre coupled together. So if you think about the distance between the two peaks of this signal, that is the coupling constant, and the coupling constant is the same for both of these signals, because these protonsĪre splitting each other. In this video, we're more concerned with the idea of the coupling constant, and the coupling constant refers to the distance between I went into much moreĭetail about this in the spin-spin splitting/spin-spinĬoupling video. The signal for the red proton into a doublet, so two peaks for the signal for the red proton. The magnetic moment can be aligned either with the external magnetic field, or against it, and that splits Signal for the blue proton to be split into two, so if I go down here, so we actually see a doublet for the signal for the blue proton.
Proton's magnetic moment can align either with theĮxternal magnetic field, or against the external magnetic field, and that causes the So here's the spectrum with no coupling, but we know that the red Signal for the blue proton, and one signal for the red proton. So let's think about first, the NMR spectrum with no coupling, so we would expect one On the same carbon, we call this geminal coupling, so geminal coupling here, so geminal, referring to the fact that both protons are on the same carbon, and coupling can occur, so those protons are close enough where they can affect each other. At the red and blue protons, they're both attached to this carbon, and if we see this double bond here, we have these different groupsĪttached to this double bond, and since there's no rotationĪround the double bond, the red and the blue protons are locked into different environments, therefore, they are NOTĬhemically equivalent, and since those protonsĪre not equivalent, they can couple together, and since this is occurring