Draw the ¹³C NMR spectrum you would expect to see for each of ...

Question

Draw the ¹³C NMR spectrum you would expect to see for each of the molecules shown.

(a) Chemical structure of methyl propanoate with a terminal alkyne group, showing bonds and functional groups.

Accepted Answer

All right. Hi, everyone. So for this question, let's go ahead and draw the estimated carbon 13 in a more spectrum of the following compound. And here we have Meth Butte three IO eight. Now recall at the number of signals when it comes to a carbon 13 in a Marsh spectrum, right? The number of signals corresponds to the number of non equivalent carbons there are within the molecule itself. So the first step is to figure out first of all how many signals we would expect to see. So if we look at the structure itself, right, notice that there is no element of symmetry present in this molecule. So because of that, right, because of that, there are going to be five non equivalent carbons within this molecule. So if I number my carbons or label my carbons, I should say a through e going from right to left. What I'll notice is that neither of them are equivalent to each other, like they're all different because this molecule has no element of symmetry to it. So since I have five carbons, I should expect to see five signals. So now let's go ahead and discuss the chemical shifts of each of these carbons. Here. Now, carbon D is connected to two different oxygen atoms in Myer. So because carbon D is next to or neighboring two electron negative atoms, it should appear the most downfield. So here, right. Carbon D because it's the carbonyl carbon of an ester recall that it generally appears. Hm, excuse me, carbon D generally appears between 160 to 185 parts per million in the carbon 13 and then more spectrum. So here from here, right, recalled my second most downfield carbon should actually be carbon B of my all kind because here, right, carbon B and Carbon A because they both come from an all kind, they both are going to generally appear between 60 parts per million. However, right, because carbon B is internal, meaning it's connected to two other carbons that is going to make it slightly more de shielded because you can compare that to carbon A that's bound to only one other carbon and hydrogen. So because carbon is more electron negative than hydrogen, by comparison, carbon B is going to appear slightly more shield, right, slightly more downfield. So that leaves us only with carbon E and carbon C to consider. However, because carbon E is part of the oxy group of our meaning it's right next to oxygen, it should be more downfield in comparison to Carbon Sea. So because carbon C is going to appear the most upfield, we can say that it's going to appear maybe at around given that it's secondary, right. Recall, it, it would appear between about 10 to 50 parts per million. Whereas carbon e considering it's connected to the oxygen of the myth oxy group recall that it should appear between around 50 to 90 parts per million. Now, it's important to recognize that some of these ranges are very close to each other and they may even overlap. So it's important to recognize that even though the range may overlap, the peaks themselves cannot, right. So always be sure to keep your peaks within these ranges, but make sure that they are a reasonable distance apart regardless. Right. So now we can go ahead and draw our spectrum and I'm going to do that by scrolling down and I'm going to start off by drawing my scale. So here I'm drawing my skill with my chemical shifts. There we go. So here I did my scale in increments of of 20 parts per million. So let me just go ahead and fix this scale. So 20 parts per million was my increment, but I'm going to add a smaller tick mark in between and I'm doing my best to keep them more or less exactly in between. So I'm just going to fix them as needed and that should be good. So the first thing I'm going to do is I'm going to draw the baseline of my carbon 13 in a more spectrum on top of the scale that I just drew and then I'm going to draw my first peak representing carbon D, which is my carbonyl carbon. So carbon D, I'm going to go ahead and draw at approximately 170. Now recall that in carbon 13 spectrum, there's no such thing as a multiple, right, all your peaks are going to appear as singlets, which is why I'm drawing one straight line and I'm going to go ahead and draw it at approximately 1 70. So up next, right up next is going to be Carbon B which is in between about 90 parts per million. But here I'm going to go ahead and draw it just before 80 parts per billion. Now, carbon A is approximately in the same range, but recall that it still has to appear more, more upfield than carbon beat, right? So I'm going to go ahead and draw it next to the peak representing carbon B, but here I'm going to draw them some distance apart. So you can see that there are two distinct peaks and then from there is Carbon E which spans between 50 90 parts per million. But again, in order to show that they are dif different peaks, I'm going to draw them a reasonable distance apart. So I'm going to draw my next signal at a round 50 parts per million and then my last one, carbon C I'm going to draw just before 30 parts from M and here I have all of my peaks and there you have it. So for each of visualization, I'm actually gonna going to go ahead and move this a little bit downwards just so you can see a better separation between the parts per million values that I wrote and the spectrum itself. But with that being said, here is the completed carbon 13 and a more spectrum. Now, the bottom line is to first and foremost identify how many peaks you would expect to see according to the number of non equivalent carbons present in your molecule. And from there, right, you can go ahead and recall your approximate chemical shift values depending on what type of carbon you have in your molecule itself. And then once you go ahead and draw your scale, you can go ahead and arrange each peak in order depending on which is the most shielded up to, which is the most shielded. So if you stuck around to the end, thank you so much for watching. And I hope you found this helpful.

Draw the ¹³C NMR spectrum you would expect to see for each of the molecules shown.
(a)

Key Concepts

¹³C NMR Spectroscopy

Chemical Shift

Symmetry and Equivalent Carbons

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