Describe the ¹H NMR spectrum you would expect for e...

Question

Describe the ¹H NMR spectrum you would expect for each of the following compounds, indicating the relative positions of the signals:

n.

Accepted Answer

All right. Hi everyone. So for this question, lets describe the expected proton NMR spectrum and indicate the relative position of the signals for the given compound. So recall first and foremost, right, that the proton NMR spectrum specifically the number of signals in a proton NMR spectrum corresponds to the number of sets of equivalent protons that are present within a given molecule. Right now, the reason why I bring up this idea of equivalent sets of protons is because at times, especially when there's symmetry associated to a given molecule, multiple sets of protons can be considered equivalent and therefore correspond to the same signal. And if we consider the compound given on the screen here, there is an element of symmetry because I could essentially draw a line down the middle of the keen here. And I'll notice that I have the same substituents on either side. So not symmetry per se, but definitely the same chemical environment because I do have the same substituents. Now, because of this my proton NMR spectrum should only yield two distinct signals because the vinyl protons on my alkene here would be considered equivalent because they do have the same substituents. And so would all of these metal groups on both my tribal substituents? So that means that we have a total number of two signals. So for each signal, there are two things that we're going to describe in order to answer this question, first is the multiplicity and second is the chemical shift. Now recall that the multiplicity deals with this concept of there being split peaks in a proton NMR spectrum because signals in proton an amar can be split into N plus one peaks where N is the number of equivalent protons connected to adjacent carbons. Now, if equivalent protons are next to each other, they would not split each other's signal. Rather, we're looking for other sets of equivalent protons. For example, right, if I consider my vinyl protons on the keen carbons, the only protons that are adjacent to any given one is itself, right? Because these two vinyl protons are adjacent to each other. Now, because of this, they won't actually split each other's signal, which means that they won't have any neighbors, so to speak, because when we discuss the N plus one rule N refers to the number of neighbors, right, or other protons that would split a given signal. So for the blue ones, right, for the vinyl ones, because the number of neighbors is zero. And when you add 0 to 1 that gives you one, this signal is going to look like a singlet in the proton NMR spectrum. So there's one single peak. And so the same thing can be said for all of our methyl protons, right, because the only other protons adjacent to them are themselves. So because there are no neighbors, so to speak, according to the N plus one rule, their signal is going to appear as a singlet as well. So now we can go ahead and discuss the chemical shift, which has to do with the location of a given signal on the actual NMR spectrum. And when we discuss the chemical shift specifically where a specific signal is found on the spectrum, right, we concern ourselves with this concept of shielding versus de shielding. So what does that mean? Right. Well, to start off, right, recalled electrons surround the protons inside of a nucleus and therefore shield it from NMR effects, shielded signals or shielded protons have more electrons surrounding it, therefore protecting it. So to speak from the NMR effects, now, shielded signals are generally going to appear far to the right side of the spectrum. And by contrast, we can also talk about the concept of de shielding because sometimes protons can be connected to atoms that are connected to electron atoms or electron withdrawing groups. And so what that does is remove electron density away from the proton itself. So when that happens, its corresponding signal is said to be d shielded and it can be found farther to the left of the spectrum. Now, with this in mind, recall, the ocular protons are among the most shielded signals that we can see on a proton in a more spectrum. So my methyl groups here in comparison to my vinyl protons are going to be relatively shielded, which means that they're going to appear farther on the right side of the spectrum as opposed to my vinyl proton because my vinyl protons due to their presence on this pipe on here are going to appear d shielded, they're d shielded because of the fact that they have a pi bond in close proximity. So when we describe the proton and more spectrum that we expect to see, we can say that from left to right, the signals that will appear in the NMR R singlet and singlet and there you have it. So from left to right, the signals that will appear in the NMR are singlet and singlet, we have two signals in total, both of which are singlets in this case. And with that being said, thank you very much for watching. And I hope you found this helpful.

Describe the ¹H NMR spectrum you would expect for each of the following compounds, indicating the relative positions of the signals:
n.

Key Concepts

1H NMR Spectroscopy

Chemical Shift

Integration and Multiplicity

Describe the 1H NMR spectrum you would expect for each of the following compounds, indicating the relative positions of the signals:n.

Key Concepts

1H NMR Spectroscopy

Chemical Shift

Integration and Multiplicity

Describe the ¹H NMR spectrum you would expect for each of the following compounds, indicating the relative positions of the signals:
n.