I watched chads but for some reason can't seem to grasp the HNmR and how he gets septets, doublets, dod etc. any good resources for this part of orgo?
Need help with multiplets
- Thread starter mjzgrk
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What you are referring to is splitting. To find the splitting for a particular hydrogen, there is this "n + 1" rule. The "n" means neighbor and it is the neighbor to the carbon that the hydrogen is connected to.
The number of hydrogens on the "n" (neighbor carbon) gives you "n". "n + 1" is the number of splits. You end up getting septets, multiplets, etc. when the hydrogen has more than one neighbor with hydrogens b/c now you have to add: (neighbor a + 1) + (neighbor b + 1).
Last tip, the area under the peaks gives you the number of hydrogens that have that same peak, or at least the ratios of the area under the peaks are equal to the ratio of hydrogens for each peak. It's easy to confuse splitting with the area under the peaks, so try and keep them straight.
Let me know if this helps at all 🙂
The number of hydrogens on the "n" (neighbor carbon) gives you "n". "n + 1" is the number of splits. You end up getting septets, multiplets, etc. when the hydrogen has more than one neighbor with hydrogens b/c now you have to add: (neighbor a + 1) + (neighbor b + 1).
Last tip, the area under the peaks gives you the number of hydrogens that have that same peak, or at least the ratios of the area under the peaks are equal to the ratio of hydrogens for each peak. It's easy to confuse splitting with the area under the peaks, so try and keep them straight.
Let me know if this helps at all 🙂
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Thanks! Okay, so on all of these images there is NO splitting. This is because the neighbor carbon to each hydrogen does not have any hydrogens on it. (Don't forget it's the neighbor to the atom that the Hydrogen is attached to). Therefore, n = 0. (n + 1) = (0 +1) which gives you all of the singlets you are seeing.
What I was explaining about the "area under the curves" correlates to the ratio of hydrogens in each peak, applies here as the height of the singlet, since it is not widened like a doublet, triplet, etc would be, creating a clear image of what you think of as area. So, for example look at the top right picture. You have 2 peaks and each peak corresponds to 3 hydrogens. This is why those peaks are the same height.
Look at the top middle one, again we have 2 peaks but you can see that one peak is 1/3 as high as the other one. This is because one peak corresponds to 6 hydrogens and the other peak corresponds to 2 hydrogens, giving you a 1:3 ratio.
Look at the bottom left one. You have 2 peaks but one peak corresponds to 9 hydrogens whereas the other only 1 hydrogen. The peaks are then in a height ratio of 9:1.
Lastly, to clear up any confusion. ANY HYDROGEN will show up in hNMR. Usually it is a C-H bond we see, but for example O-H bonds will also show up. In the bottom middle image above you can see that there are 3 peaks. One of those peaks is from the Hydrogen in the alcohol. The other 2 peaks correspond to the CH3 and the C-H. From what I just explained, maybe you can guess that the 2 peaks that are about the same height must correspond to the C-H and the O-H, since they both only have one Hydrogen. The other peak is about 6 times taller because it consists of the 6 Hydrogens in the two CH3 groups.
What I was explaining about the "area under the curves" correlates to the ratio of hydrogens in each peak, applies here as the height of the singlet, since it is not widened like a doublet, triplet, etc would be, creating a clear image of what you think of as area. So, for example look at the top right picture. You have 2 peaks and each peak corresponds to 3 hydrogens. This is why those peaks are the same height.
Look at the top middle one, again we have 2 peaks but you can see that one peak is 1/3 as high as the other one. This is because one peak corresponds to 6 hydrogens and the other peak corresponds to 2 hydrogens, giving you a 1:3 ratio.
Look at the bottom left one. You have 2 peaks but one peak corresponds to 9 hydrogens whereas the other only 1 hydrogen. The peaks are then in a height ratio of 9:1.
Lastly, to clear up any confusion. ANY HYDROGEN will show up in hNMR. Usually it is a C-H bond we see, but for example O-H bonds will also show up. In the bottom middle image above you can see that there are 3 peaks. One of those peaks is from the Hydrogen in the alcohol. The other 2 peaks correspond to the CH3 and the C-H. From what I just explained, maybe you can guess that the 2 peaks that are about the same height must correspond to the C-H and the O-H, since they both only have one Hydrogen. The other peak is about 6 times taller because it consists of the 6 Hydrogens in the two CH3 groups.
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Final note: I often think that the peak I see at the "O" mark is a peak. Just make sure you don't ever count a peak at the Zero mark. I once got confused on a destroyer problem because of this.
