The following ¹H NMR spectra are for four compounds...

Question

The following ¹H NMR spectra are for four compounds, each with molecular formula of C₆H₁₂O₂. Identify the compounds.

c.

Accepted Answer

Hello everyone. Let's do this problem. It says the proton N M R spectrum below is produced by a compound with the molecular formula C five H 10 02. What is its structure? And we are given four answer choices. Answer choice A has the structure of isopropyl acetate. Answer choice B is methyl butyrate. Answer choice C is ethyl propionate and answer choice D is iso butyl form. So when we are given a proton N M R spectrum, there are various characteristics of the spectrum that can help us decide what the structure of our compound is. So some of those characteristics are the number of signals which tells us how many unique proton groups that we have on our structure. We have the integration of the signals which are given to us here right from left to right, we have one hydrogen, two hydrogens, one hydrogen and six hydrogen for our four signals. And that tells us how many hydrogens are represented by that signal. We have the multiplicity which follows the expression N plus one. And that tells us how many neighboring protons we have, right N is the number of neighboring protons to the proton in question. So we will have either a singlet doublet triplet, et cetera. And lastly, the chemical shift of the signal will gives us will give us clues about what is nearby that proton, right? Because if that proton is next to, let's say an electron negative atom like oxygen, that electron negative oxygen is going to draw the negative electrons towards it, which will make those hydrogens naked, right? They will be DeShields. So then they will have a higher chemical shift. OK. So first I like to do this in order. So going through each of these characteristics in order to help us narrow down our answer choice, right? Work smarter, not harder. So how many signals will each of these answer choice structures give us starting with answer choice. A we have one signal for this methyl group, two for this methane protein and three for these two equivalent methyl groups. Well, that's only three signals and we know our spectrum has four signals. So we know answer A is incorrect. OK. What about structure B? We have 1234 signals. OK. That's a possibility and answer choice. C we have 1234 signals as well. Answer choice. D one for both of these methyl groups, two three signals for that aldehyde proton, right? Oh And 1/4 1 for that meine proton there. So that is four signals as well. OK. So we eliminate one answer choice. Now let's move on to integration. So let's see how many protons are reflected by each of these signals in these structures. So starting with answer choice B, we have proton one, signal two, signal three and signal four. So signal one represents those three methyl protons. So that will have an integration of three H answer choice two represents two protons that methylene group answer choice three, another methylene group. So two hydrogens and answer choice four, another methyl group. So we have 322 and three hydrogens. Does that match the integration of our signals in our N M R structure? No, right. We have 121 and six. So just by looking at the integration, we know answer choice B is incorrect. Let's do the same for answer choice C for signal one, we have three hydrogens that methyl group four, signal two, we have two hydrogens for that methylene group and same four signals three and four. Signal three is two hydrogens. Signal four is three hydrogens. So we know answer choice C is incorrect. So by process of elimination, we know that D is going to be our correct answer. Let's double check the integration and the other characteristics. So starting with I'm going to number these in order. So 234. So signal one, we have those six protons from those two methyl groups. OK. That's starting to look like our spectrum signal two, we have a singular proton, one proton that methane group signal three has two hydrogens signal four has one hydrogen that aldehyde hydrogen and that matches the integration of our spectrum, right 6121. And notice how this one, this integration of this singlet with one proton is all the way pretty far downfield right around eight P PM. That's going to be reflective of our aldehyde proton which we see in this structure. And we don't see that in any other structure. So that's another hint as to why this answer is correct. Let's quickly go over the multiplicity as well. If you want to stick around and see why that is also part of the correctness of this answer. So signal one, the six hydrogens are neighboring one proton. So that should be a double it, right? One plus one is two, signal two has 678 neighboring protons that is going to be a multiple. And those are all non equivalent protons, right. The methylene protons are different than the methyl proton. So that will have a whole splitting ordeal signal three has one neighboring proton. So that will be a doublet and the aldehyde proton has no neighboring hydrogen. So that will be a singlet. So our six H signal is a double it, our upfield one H signal is a multiple, our two H signal is a doublet and our one H signal is a singlet. And that all again lines up with answer choice D and chemical shift. Lastly, we mentioned that aldehyde proton makes sense why it's more upfield or sorry, why it's way more downfield than the other signals then signal three, our methylene protons are directly next to that oxygen atom. So that makes sense why they are more downfield than the other two signals. And as we get further away from the oxygen atom, our signals are more upfield, right? So with all of that said, once again, answer choice D or Iso Beyl format is the correct structure and correct answer for this problem. That's it for this one. I hope this video is helpful and thanks for watching.

The following ¹H NMR spectra are for four compounds, each with molecular formula of C₆H₁₂O₂. Identify the compounds.
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Key Concepts

1H NMR Spectroscopy

Chemical Shifts

Integration and Multiplicity

The following 1H NMR spectra are for four compounds, each with molecular formula of C6H12O2. Identify the compounds. c. <IMAGE>

Key Concepts

1H NMR Spectroscopy

Chemical Shifts

Integration and Multiplicity

The following ¹H NMR spectra are for four compounds, each with molecular formula of C₆H₁₂O₂. Identify the compounds.
c. <IMAGE>