The ¹H NMR spectrum of 2-propen-1-ol is shown here....

Question

The ¹H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.

Accepted Answer

Hello everyone. Let's do this problem. It says assign the protons responsible for each of the signals in the proton N M R spectrum for 24 dimethyl three pinol. Now there are a few characteristics of the proton N M R spectrum that we can use to identify the protons on our compound. So the first one would be simply the number of signals that tells us how many equivalent proton groups we have on our structure. The integration of the signals which tells us how many protons are attributed to that signal. And we are given those integrations specifically 12 hydrogens, two hydrogens, one hydrogen, one hydrogen, we have the multiplicity. So is the signal, a singlet doublet triplet and multiplicity is given by the function N plus one where N is the number of protons, the number of neighboring protons, right. So the number of protons next to the proton in question, and lastly chemical shift, which is based on the relative location of that proton, right? Because recall that protons in an electron poor environment are going to be de shielded, which will result in a higher chemical shift. So for example, if we have an electron negative atom like oxygen, that electron negative atom is going to draw in the electrons towards it, which will decrease the electron density around that proton making it more naked or de shielded. Right? I it's helpful for me to think of that proton as being naked without electrons around it. All right. So let's look at the structure of our compound. 24 dimethyl three pinol. So the root is pinol, which we know is five carbon. So let's draw a five carbon chain 12345, we have an alcohol group on carbon three given to us by the O L ending on fentaNYL. And I'm going to draw out all the hydrogen. So we can label their chemical shifts. We have 24 dimethyl. So one methyl on carbon 21 methyl on carbon four. And now let's draw out all the hydrogens. I'm going to draw out first, the ones that are attached to the carbon chain. So the singular proton on carbon two, the singular proton on carbon three and the singular proton on carbon four and now all of the methyl protons. So the methyl protons on carbon one on carbon five in on our two methyl groups. So notice we have a lot more than four protons, right? Even though we have only four signals. So that tells us that we have some chemically equivalent protons. The most notable one in our spectrum is this large signal just below one P PM, which has an integration of 12 hydrogens. So we do have four methyl groups, right, and each methyl group has three protons. So I think all of those methyl protons are going to be chemically equivalent. And it makes sense because our compound is symmetrical, right, write down carbon three, we can slice it in half. So both sides are symmetrical and those methyl groups are both coming off of carbons two and four, right, if we look at carbons one and five as a methyl substituent group, they are both coming off of carbons two and four. So let's label all 12 of those protons with the chemical shift of 120.91. And let's talk about some of the other characteristics that I mentioned. So chemical shift, these protons are the furthest away from that electron negative oxygen, right? So it makes sense that they have the lowest chemical shift and they only have one neighboring proton. So one plus one is two, making it a doublet. All right. So that takes care of most of the protons actually. So let's look at the alcohol proton, that's going to be an easy one to identify from the spectrum because that hydrogen is directly attached to the electron negative oxygen. So this should be the most naked and most DeShields proton, which will make it have the highest chemical shift. So if we look at our most downfield proton, it does have an integration of one hydrogen So that is going to be the signal for this alcohol proton. And that has a chemical shift of about 3.58. All right. Now, it's easier to narrow down our other two signals because we have this singular proton on carbon three and then the car, the protons on carbons two and four are equivalent, right? Because of the symmetry. So the singular proton on carbon three is going to be the signal at 3.19 P PM. And it's a triplet because we have those two protons on carbons, two and 42 plus one is three, making it a triplet. And lastly, those two methane protons on carbons two and four are the multiple at around 1.92. And this is a multiple because it has all of those neighboring methyl protons, right. So that is the structure of 24 dimethyl, three pinol with all of the protons assigned their chemical shift. That's it for this problem. I hope this video is helpful and thanks for watching.

The ¹H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.
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Key Concepts

Proton NMR Spectroscopy

Chemical Shift

Integration and Multiplicity

The 1H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.<IMAGE>

Key Concepts

Proton NMR Spectroscopy

Chemical Shift

Integration and Multiplicity

The ¹H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.
<IMAGE>