Show how you would distinguish among the following three compo...

Question

Show how you would distinguish among the following three compounds

(a) using infrared spectroscopy and no other information.

(b) using proton NMR spectroscopy and no other information.

(c) using ¹³C NMR, including DEPT, and no other information.

Accepted Answer

All right. Hi everyone. So for this question is asking us how the following compounds can be distinguished using only the techniques listed below and no other information. So for part one we have only proton NMR spectroscopy. So what's going to be um common or rather what all three molecules are going to have in common is the fact that they're going to have four peaks within the aromatic region. Because notice how all three molecules have to substitute prints in the meta position relative to each other and they're not the same right? They each have different substitue ints, which means that there's no symmetry. So each proton in the aromatic ring here is going to be unique. Therefore it's going to yield a different signal. But our substitute parents can give us the information that we need to figure this out. Right. So for part one Or infrastructure one, I should say we have an all the hide on the right side and an ether on the left side with a methyl group. So, recall that your alba hide. proton appears Generally at around 9-10 parts per million. And it's a single it that's going to be very sharp. Alright. It's characteristically very sharp. Now, as for the methyl group of our ether here on the left side, it's going to be bonded or rather it is bonded directly to oxygen, which is electro negative. So that means that these protons of the method group are going to be relatively d shielded. So they're going to show up more downfield or more to the left side of the spectrum. So recall that when we have a situation like this where um the carbon is bonded to oxygen directly. Then its protons are going to appear At around 3. to 3.8 PPm. You can't see that cut off. There we go PPm. So that's going to conclude our discussion for a structure one. So now let's talk about structure to and structure to has a carb oxalic acid on the right side, with a methyl group on the left side. So the C. O. H. Group has a very distinctive signal. Right recall that carb oxalic acids. Its proton is going to be a very broad singlet in between 10 to 14 parts per million. Right? It's incredibly downfield because this proton is incredibly D shielded. So that's a crab oxalic acid. But our mental group, unlike structure one, it's bonded directly to the Benzene ring. So it's actually going to be more upfield or rather to the right side of the spectrum at around maybe 2.4 parts per million. More or less. So that's infrastructure too. And now for structure three, Structure three has an ester on the right side with the Methyl group and an alcohol on the left side. So the alcohol recall that the um the hydroxy proton of your alcohol is also going to be a broad single. It like your carb oxalic acid but it's going to be slightly more upfield. Right. It's going to show up between maybe 9 to 10 parts per million as opposed to 10 to 14 for a carb oxalic acid. But our method group, our method group of our Esther here is similar to the method group of our ether in structure one, right? Because they're both bonded directly to oxygen. Which means that that carbons protons are going to be more D shielded. Therefore at around 3.7 to 3.8 parts per million. So that concludes our discussion for proton NMR. And now we can proceed to part B, which is going to be carbon 13 NMR with D E P T. Experiments. So what we have, well for this molecule we're going to have Carbonneau carbons for each. Right? But the fact that they're different functional groups is going to be the key for us to tell them apart. Right? So recall that infrastructure one that carbonnel carbon of your Aldo hide Shows up generally at around 190 parts per million In a carbon 13 spectrum. Whereas structures two and um those carbons, carbons Show up at around parts per million. So that is how you would tell um Those two, those 3 apart. So now if I scroll down for part C to give myself some space, we can talk about infrared spectroscopy to tell all three of these substances apart. So all three of these structures are going to have C double bond C stretches associated to their benzine ring and they're also going to have stretches associated to that carbonnel group. However, for structure 1 1st of all, the C. H. Bond of the alga hide. So C. H. Alpha hide recall that it's going to give us two signals, right? We're going to see one at around 27 10. And we would also see another peak at around 28 10 inverse centimeters. So that's going to be you're all the high. And on the other hand, infrastructure to recall once again that carb oxalic acids have a very characteristic IR structure, right? Because the O. H. In particular of the IR is going to take up so much of your spectrum. Right? So this characteristic C. O. H. Peak that you're gonna see in the spectrum It's gonna show up between 2500 2 30 500 inverse cm. With his shoulder with shoulder at around inverse centimeters. So that's gonna be infrastructure too. Now, structure three has the characteristic O. H. Signal right? For an alcohol not a carb oxalic acid. So for an alcohol you're going to see an incredibly broad peak In between around 30 100 to 30 500 inverse centimeters. But it's not going to be anywhere near as broad as your as your crab oxalic acid. Right? But it's still going to be pretty broad. So that is going to be it for this question. And with all this being said, your answer choice is going to be choice A and that is going to be your answer. Thank you very much for watching if you made it to the end of this video, and I hope you found this helpful.

Show how you would distinguish among the following three compounds
(a) using infrared spectroscopy and no other information.
(b) using proton NMR spectroscopy and no other information.
(c) using ¹³C NMR, including DEPT, and no other information.

Key Concepts

Infrared Spectroscopy (IR)

Proton Nuclear Magnetic Resonance (1H NMR)

Carbon-13 Nuclear Magnetic Resonance (13C NMR) and DEPT

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