Questions tagged [nmr-spectroscopy]
This tag should be applied to all questions about nuclear magnetic resonance, including the underpinning theory and the measurement or interpretation of spectra.
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NMR for diamagnetic uranium molecule's isotopic enrichment
Inspired by Dr. Raizen's MAGIS isotope enrichment scheme, I looked for another way.
While uranium elementally has unpaired electrons making its nuclear magnetic moment much weaker than electron ...
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1H NMR of phosphonic acid
I am working on synthesis of an alkyl bromide from alcohol by action of $\ce{PBr3}$. The product has a limited solubility in DCM, thus isolation by filtration of the product seems to be a better ...
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Distance between peaks in 1H-NMR multiplets
In discussing coupled spins, OpenStax Organic Chemistry shows the following NMR spectrum:
The figure caption claims that "the distance between peaks is the same in both multiplets". They don'...
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Reason for 19F NMR of OsO2F3 chemical shift
I have been learning that the $\ce{^{19}F}$-NMR spectrum of $\ce{[OsO2F3]^+}$ cation shows two sets of signals. There is a doublet and a triplet which accurately depicts that there are two axial ...
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NMR pulse sequence for precise measurements of coupling constants?
The usual procedure for measuring $J$ coupling constants in NMR is to record a 1D spectrum and estimate the constant from the differences of peak frequencies. Fitting the spectrum to a lineshape ...
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What are the units of equation 13 of Buckingham's 1960 paper about chemical shift influenced by electric field?
Has anyone read Buckingham's 1960 paper 'CHEMICAL SHIFTS IN THE NUCLEAR MAGNETIC RESONANCE SPECTRA OF MOLECULES CONTAINING POLAR GROUPS'? I'm having trouble understanding Equation 13 regarding the ...
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Precessional frequency in H-NMR
Suppose we have a hydrogen nucleus. Now, let's apply an external magnetic field $B$. As the magnetic field is applied, the hydrogen nucleus undergoes precessional motion about its own axis with ...
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How to theoretically derive phased spectra in NMR?
I came across the following question in my NMR course for chemists:
Assuming that magnetization along the y-axis gives rise to an absorption mode
lineshape, draw sketches ...
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What causes the four proton signals closest to the carbonyl in tetraphenylcyclopentadienone to appear more upfield than the other 16 aromatic protons?
What causes the four proton signals closest to the carbonyl in tetraphenylcyclopentadienone to appear more upfield than the other 16 aromatic protons? It's my current understanding that the carbonyl ...
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H-NMR: Why do certain protons couple despite being further away and vice versa?
I just started learning about $^1\ce{H}$-NMR. Recently, I studied chapter 13 in Organic Chemistry by Clayden, et al. (Ref.1; specifically pp. 295-298) and came across the following graphic:
I am ...
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H-NMR: Why are coupling and integration values not matching?
I am trying to synthesize Ethyl 2-(triphenylphosphoranylidene)propionate.
I recently ran an NMR which is attached below.
I am ignoring impurities for now.
Considering the ethyl group, the number of ...
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What is the difference between 2,6-di-tert-butyl-4-methylphenol and 3,5-di-tert-butyl-4-methylphenol 1H NMR spectra?
So there was this exercise in my book (picture below) a compound
I got to the conclusion that the compound might be either 2,6-di-tert-butyl-4-methylphenol or 3,5-di-tert-butyl-4-methylphenol. I was ...
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Chemical exchange for N,N-dimethylnitrosamine isomers in NMR [duplicate]
Apparently the NMR of the methyls of N,N-dimethylnitrosamine isomers show a different chemical shift in NMR, which can lead to coalescence depending on temperature.
Since the molecule is symmetric on ...
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Why does epsilon caprolactone not have triplets on 1H NMR?
Looking at the structure of epsilon caprolactone (CL), you'd assume that the methylene protons (CH2) on either side of the ester would give you triplets. However, experimentally those peaks actually ...
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Difference in 13C NMR spectrum
The tasks proposed in Spectroscopy challenge, I found two structures that are mostly similar in allylic moiety, the contradiction is presented below:
Considering two carbons of the alkene bond, it ...
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Carbonyl and thiocarbonyl 13C NMR
According to this paper, the deshielding effect of C=S group is specifically due to the delta(11), which is the least shielded component. However, the conclusion tells me that this component is ...
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Why do protons in same chemical environment do not exhibit spin-spin coupling?
Reading introductory tutorials on proton NMR for the determination of chemical structure, I was told that protons can exhibit spin-spin coupling, thus creating multiplets on an NMR graph. The coupling ...
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2D NMR of a Funky Disaccharide
Below you'll find the structure of the disaccharide and three 2D NMR spectra - COSY, HSQC, HMBC. I have to match the signals in the spectra to the nuclei that caused them. Answers to any subset of the ...
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Multiplicity and signals of cis−[(Ph3P)2PtF2] in two NMR spectra
I am interested in the number of the signals and their multiplicities in the $\ce{^{31}P\{^1H\}}$ and $\ce{^{19}F\{^1H}\}$ NMR spectra of $\ce{[\textit{cis-}(Ph3P)2PtF2]}$. It is given that $\ce{Pt}$ ...
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Why would 1-ethenyl-2,6-dimethylbicyclo[2.2.0]hexane give off 8 H1 signals?
I am trying to figure out this problem, and can only find seven signals, two from the double bond, one from the single bond attached to the double, there is symmetry, so one signal on the methyl, one ...
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Which group is more ortho/para-directing?
Currently working on assigning the C NMR and H NMR spectra for this molecule (I believe it's called E-E bis(4-methylbenzylidene)acetone ) but I'm a bit confused as to whether the methyl group is more ...
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Why do t-butyl and isopropyl groups deshield the ipso carbon in C13 NMR more than a Me group?
I have a t-butyl group attached to an aromatic ring and I am confused about why it increases the shift of the ipso carbon about 20ppm. I know that C is slightly more electronegative than H, and this ...
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Carbon 13 NMR peaks - ketones
Why the shift of acetophenone's carbonyl carbon at C13 NMR spectrum is larger than the equivalent peak at trifluoroacetophenone ? Particularly , the first one is located at 197.94 ppm whereas the ...
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What is molecular "tumbling" in NMR?
In NMR textbooks, it is often said that small molecules tumble faster and large molecules tumble slower. What is "tumbling" exactly? When I searched for it, someone says that it is any ...
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Assignment of NMR peaks of polystyrene
I’m having trouble identifying the peak around 3,75 ppm in the 1H-NMR spectrum of polystyrene measured at 400 Hz in CDCl3. Could someone please provide their perspective on it? I see it appear in a ...
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NMR splitting of equivalent, but separated protons
I’ve been trying to understand why equivalent sets of protons that are coupled behave as equivalent to a single coupled pair. For example in the spectrum for Diethyl ether:
Both groups of Hb are ...
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Predicted H NMR spectrum shows two signals for NH2 group
There are two singlet signals for NH2 group around 2.4 and 3.05 ppm. Spectra is predicted (from MNova), so there was no water present. Why the signal of NH2 group isn't a broad singlet?
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Why are different Aluminium valencies observed from NMR and what logic can be used to normalise molar ratios of different valency atoms?
Question 1:
I've observed different chemical shifts in 27Al Nuclear Magnetic Resonance (NMR) spectra of commercial aqueous sodium aluminate, indicating the presence of both trivalent [Al(III)] and ...
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How to determine the value of the NOE from the NOESY spectrum?
I have 1D NOESY spectra from which I need to find out the value of the NOE (%). Is it enough to simply measure the intensity of the resulting peaks or is it necessary to subtract it from the ...
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H-NMR Analysis of C15H24O
I was able to figure out that the structure of this compound was a benzene ring with 2 equivalent trimethyl groups to give the 18H singlet. Another non-equivalent methyl group to give the 3H singlet. ...
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31P-13C coupling in bis(diphenylphosphino)methane
In the 13C NMR spectrum of bis(diphenylphosphino)methane (dppm), some of the phenyl carbon signals appear to be split into triplets. It makes sense to me that the center methylene is split into a ...
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What shifts protons on a benzene ring to lower ppm?
Why do these protons appear at 6.9 and 6.93 ppm, at lower ppm value? I assumed it was due to the anisotropic effect, specifically I thought the circulating (pi) electrons induced a magnetic field ...
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Interpreting NMR: what does it mean when there are two signals when there should be (and looks like) only one, and integration where there is no peak?
A couple of basic questions.
So in this spectrum, there seem to be two peaks at 2.38-2.347, but this signal should be a singlet and correspond to the methyl group. So does this mean anything?
Another ...
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NMR and dienes to isolate certain isotopes?
I am looking to achieve isotope separation using transition states.
In the rxn of dienes with halogens, based on the temperature, the dienes can create a thermodynamic product or a kinetic product. ...
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evaporating DMSO/Ethanol
I'm preparing to do a thiolclick reaction and to get a homogenous phase I found it's best to use DMSO/ethanol as solvent for the -ene and thiol reagents. I need the ethanol specifically for hole-...
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What could be the origin of a persisting distorted water NMR signal?
I am currently running some solvent suppression experiment on water samples. I first run a one scan 1H experiment to get the ''O1P'' and then implement it in the solvent suppression experiment (''...
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How to read 1H-NMR- and IR-spectre (for ibuprofen) [closed]
I have read the answers to related/similar questions. They didn't help.
I have to read a proton-NMR-spectrum and an IR-spectrum of ibuprofen. The structure formula is given to:
I have not been ...
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What's the exact mechanism of spin coupling in NMR?
The most common one that's found nearly in every textbook and site is that splitting occurs due to the alignment of neighboring proton either with or against the external magnetic field so as it's B ...
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Why are fluorine-19 NMR spectra less affected by paramagnetic centers than other common nuclei?
I know that 19F NMR spectra are less sensitive to paramagnetic centers as an empirical fact: it’s my experience and that’s what people in my lab have always been saying.
For instance, some of my ...
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1H-NMR: How does the oxygen in ethers act as a spin coupling barrier while the oxygen in hydroxy groups doesn't?
It is possible to observe coupling between a hydroxyl proton and other protons. Why does the oxygen atom in ethers prevent any further coupling and act as a sort of barrier between spin systems? Or is ...
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NH protons not appearing in H NMR spectrum of 3,4-dihydropyrimidone derivative (solvent: CDCl3)
My synthesized compound is 3,4-dihydropyrimidone derivative, which has 2 nitrogen in the ring. The $\ce{NH}$ protons are not appearing in the H NMR spectrum and the solvent used was deuterated ...
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How to interpret this pair of IR and 1H NMR spectra?
I need to figure out the structure of a $C_{8}H_{14}O_{2}$ molecule with this IR spectrum:
and these $^{1}$H NMR spectrum signals:
m means 4 or more spikes.
I worked out that the degree of ...
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Which Hydrogen in this structure is more deshielded/shielded?
Looking at the 2 hydrogens connected to the Carbon-carbon double bond, which hydrogen is more deshielded or shielded?
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Why has acetaminophen only two different NMR chemical shifts related to phenyl?
I learned that, by using NMR, you could tell how many different hydrogen environments an molecule has. For example, benzene has only one.
Since acetaminophen has an amide bond, and the bond has ...
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Why are the protons of ethene magnetically equivalent?
According to this website,
For two protons to be magnetically equivalent they not only have to have the same chemical shift, but they must also each have the same J coupling to other magnetic nuclei ...
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Fermi Contact Interactions and resultant coupling contants
I am currently learning about spin-spin coupling mechanisms and have become very confused about the mechanisms by which spin-spin coupling happens in NMR.
I understand how we can draw diagrams where ...
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NMR Assignment of cinnamaldehyde
I'm struggling to understand the assignment of the aromatic protons in this compound. Based on the simulated spectra (and lit spectra), the three protons on the left are all overlapping. To the best ...
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Why is a ring carbon C-R of a substituted ferrocene more downshifted on 13C-NMR?
Upon assigning $\ce{^{13}C}$-NMR for 1,1'-bis(α-methylmethanol)ferrocene, we discovered the substituted FcC-CH peak (95.14 ppm) was more downshifted than the CH-OH peak (65.59 ppm) as was confirmed by ...
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Reconstruction of NMR spectrum by entropy maximization (MaxEnt)
Currently NMR spectra are generated by Fourier transformation of free induction decay curves from time domain to frequency domain. In the late 60 s-80s some researchers proposed reconstruction of NMR ...
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Why does population difference matter in NMR
I know that population difference matters in NMR for sensitivity, that the splitting is dependent upon the gyromagnetic ratio of the nucleus, and that the population of the spin states is almost ...
