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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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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What's the current of an aromatic ring?
Aromatic molecules like benzene have a ring current, created by the movement of electrons around the ring. This is most visible during proton NMR, when the magnetic field of the ring current opposes ...
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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: What parameters influence spin-spin coupling between protons, and why?
I'd like to better understand spin-spin coupling. What other mechanisms are there besides fermi contact interactions? How are the different mechanisms influenced by different parameters like ...
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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 ...
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Regioselectivity in oxo-Diels-Alder reaction
I have one doubt about the dimerization of methacryloyl chloride into the product 3:
The dimerized product was observerd around 10-15mol% in different commercial samples of methacryloyl chloride, as ...
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Tips on understanding one-bond J couplings in NMR
I have just started a spectroscopy course in nuclear magnetic resonance, which I have loved thus far, but have been extremely puzzled regarding 1J coupling constants.
I was wondering if any of you had ...
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Can proton NMR be used to study transition metal complexes?
I prepared metal complexes with a Schiff base ligand L using cobalt(II) chloride hexahydrate, iron(III) chloride hexahydrate, and nickel(II) nitrate hexahydrate. I used 1H NMR to study the difference ...
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Phenol's resonance structure doesn't match NMR
I've asked a question before and quickly realised that the resonance/mesometric effects played a large role in determining the C-13 NMR spectrum of phenol, shown below.
This is the resonance ...
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How many hydrogen environments are there in phenyl acetic acid? [duplicate]
How does the molecule below have only three hydrogen environments? Should it not have 5 different hydrogen environments according to the labelled diagram?
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Can two S=1/2 centers have J and D parameters simultaneously?
I am new to EPR/ESR and need some help in connecting theory with a published experimental data. Following is my query.
What I understood from EPR theory is that two active EPR centers with S=1/2 ...
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Why does heavy water have two different solvent peaks with DSS and TSP?
I was going through the NMR solvent peaks chart of Cambridge isotope laboratories (PDF) and I noticed that $\ce{D2O}$ had two solvent peaks: one at 4.8 with sodium trimethylsilylpropanesulfonate (DSS) ...
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What is it about nuclei with low gyromagnetic ratios that make them unreceptive in NMR?
I'm having some trouble rationalizing why nuclei with low gyromagnetic ratios are considered unreceptive in NMR. I know it's because it will take a higher magnetic field to "hit" its Larmor ...
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Considering the odd mass number rule, how does $\ce{^{14}{N}}$ NMR work?
In my high school chemistry class, we learned that NMR only works for nuclei with odd mass number. Hence, we often use the $\ce{^1{H}}$ and $\ce{^{13}{C}}$ spectra. However, on this page about NMR I ...
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NMR spectroscopy nomenclature: induced vs local vs effective magnetic field (B)
This is a simple question but I can't seem to find a place where they use the same nomenclature... I was wondering whether these are all the same thing: $B_\mathrm{induced}$, $B_\mathrm{local}$, $B_\...
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What is the relationship between Ha and Hb in the given compound, trans-1,3 dichlorocyclobutane. Are they enantiotopic or homotopic?
The question is to find the TOPICITY relationship between Ha and Hb in the given compound, (trans 1,3 dichlorocyclobutane)
They seem to be in the same chemical environment, so I tried the ...
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Why am I getting a triplet instead of a singlet on NMR for aryl HH2-group?
I am trying to interpret an $\ce{^1H}$-$\mathrm{NMR}$ spectrum on the molecule 4-amino-N-(2-chlorophenyl)benzenesulfonamide that I produced in a lab session. I have managed to assign all the hydrogen ...
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Free induction decay acquisition in NMR
Recently, there was an interesting Q&A exchange on free induction decay acquisition in NMR Is intensity in NMR spectra acquired at regular time intervals? with useful answers. I have not acquired ...
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Is intensity in NMR spectra acquired at regular time intervals?
I'm writing a parser that reads fid binary files and ASCII procpar files from FT-NMR experiments, most of them acquired using ...
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Are there any papers illustrating carboxylic acids displaying J-coupling of CH to the OH protons?
I understand that ethanol will display a J-coupling to the OH proton if observed in the absence of water, but are there any papers showing how to find this J-coupling (a 3-bond H-H J-coupling between $...
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How to determine positions of groups on compound based on H-NMR spectroscopy (C9H13NO)
Based on the below $\pu{200 MHz}$ $\ce{^1H}$-$\mathrm{NMR}$ spectroscopy, I have to determine the molecular structure of compound $\bf{B}$, which oxidises to a compound $\bf{A}$ with molecular formula ...
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How can a 90 degree pulse cause precession perpendicular to the applied field in proton NMR
From my understanding, a proton's magnetic moment in an NMR experiment can undergo precession in only two discrete states: either parallel to the applied magnetic field, or antiparallel to it. ...
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Definition of an internal reference
Warning: extreme pedantry.
I am performing Gutmann-Beckett experiments, basically utilizing an NMR-tube with my sample and a 31P-lewis base (e.g. triethylphosphine oxide) inside another one with a ...
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Hydrogens of cyclohexanol are enantiotopic or diastereotopic, which is true?
I am studying spin-spin coupling theory in NMR. Below is an exercise from Mcmurry's organic chemistry.
The textbook says that * stands for chiral center. But is it true? When I searched for it some ...
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Identifying an alkyl bromide from NMR information
This question appeared on an exam and I translate it into English.
In the NMR $\ce{H^1}$ spectrum of a pure substance, with molecular formula $\ce{C4H8Br2}$, the following chemical shifts (in ppm) ...
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Why do electron-withdrawing groups deshield outer ring protons?
I understand that ring protons experience deshielding because the induced magnetic field (outside the ring) has the same direction as the external applied field, but shouldn't electron withdrawing ...
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NMR spectrum with impure solvents [closed]
How to find the proton signals of CHCl3 impurities in NMR spectrum recorded in CDCl3? What are their intensities?
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Why do the splitting pattern on my NMR differ from those stated in literature?
I attempt the synthesis of p-toluic acid using the Grignard reagent (prepared from 4-bromotoluene and Mg) and dry ice. The NMR of the raw product was recorded using $\ce{CDCl3}$ and a peak showing ...
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NMR terminology: "Transients"
I was reading a paper on hyphenating a gas chromatograph with an NMR. The authors describe a proof-of-concept type instrument. We have a couple of NMR experts here in SE, hoping to get some insight. ...
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