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 Inductive effect of Carbon single and double bonds with Oxygen

I am trying to determine and understand the chemical shifts on NMR of the B and C carbons. Although it is quite obvious, I am trying understand why the inductive effect of the oxygen with the double ...
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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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1 answer
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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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Why is the NMR result for my p-toluic acid product so odd?

I just started learning about NMR and did a lab session where we conducted Grignard rxn with CO2 to form p-toluic acid and my NMR result is: 1H NMR (400 MHz, CDCl3) δ 9.63 (s, 4H), 8.07 – 8.00 (m, 5H),...
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Which of these protons are equivalent? Which NMR signals correspond to which protons?

Here are is the NMR spectrum and the compound (both images are the same spectrum, just close up). I know the deshielded signals are the aromatic protons and the ones ~6ppm are the alkene protons but ...
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How to generate a Hadamard Gate in Spin 1 NMR?

I am studying about the gate controllability of Spin 1 systems and I would like make a Hadamard gate using only X,Y rotations and the offset. I want to do this without invoking techniques for making ...
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Two different definitions for chemical shift (NMR)

Looking online I seem to have found 2 different definitions for chemical shift $\delta$ (in the context of NMR). The first definition uses the chemical shift of the reference in both the numerator and ...
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Is there any magnetic resonance spectroscopy that based on orbital angular momentum?

The different momenta of electron and nucleus are described by different quantum numbers. (a) l and m$_l$ describe the orbital angular momentum and quantization on its component along an arbitrary ...
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2 votes
2 answers
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Elucidating an unknown compound using 1H- and 13C-NMR spectral data [closed]

I am currently struggling with the following NMR spectrum for this compound: I know for sure that we should multiply the integrals of the hydrogen atoms by four, and that the compound contains at ...
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1 vote
2 answers
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Just looking for some help with finding relative ratios of components in a mixture using proton NMR

G'day, I am used to identifying molecular structure in isolation using proton and carbon NMR, but have never worked with a mixture before. The mixture relates to the following spectrum: The spectra ...
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Can resonance structures account for NMR spectroscopy chemical shifts?

I am unable to understand why the alpha carbon to the carbonyl group is of lower chemical shift compared to the beta carbon based on the effects of electronegativity and hybridisation. Since if ...
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How to make standard sample for NMR signal-to-noise ratio

I want to make a sample for proton NMR signal-to-noise-ratio measurement. It is conventional to use 1% ethylbenzene in d-chloroform, as specified here. I have two questions: What is meant exactly, by ...
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Why is the 2-bond (Sn-H) coupling constant larger than the 3-bond Sn-H coupling constant for tetraethyltin?

I was looking at the NMR spectrum of tetraethyltin [$\ce{Sn(CH2CH3)4}$], and found that the $\ce{Sn-H}$ coupling constant between $\ce{Sn}$ and $\ce{CH2}$ is larger than that between $\ce{Sn}$ and $\...
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NMR spectrum chemical shift confusion

Recently started on NMR spectrum, and I'm slightly confused about chemical shifts and their connection to the resonance frequency and magnetic field. From what I know, the "new" way of doing ...
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1 answer
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Does the amplitude of the RF pulse affect the NMR signal?

I know that the NMR signal depends on the static magnetic field strength $ B_0 $ (by Boltzmann equation) and its gyromagnetic factor. While NMR occurs when the RF pulse frequency matches the equation: ...
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Which atoms in indole possess the greatest amount of electron density?

Presumably the amine acts as an electron donor, but that would suggest extra electron density of the adjacent carbons, making them more shield, which isn't seen in the results in the image below. ...
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Why does the addition of heavy water cause OH and NH peaks in NMR spectra to disappear?

When $\ce{D2O}$ is added to a sample, the OH and NH peaks in a $\ce{^1H}$ NMR spectrum disappear. This is the basis of (for example) the $\ce{D2O}$ shake test, and is also the reason why peptide/...
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Find the structural compound from carbon and proton NMR spectrum

The proton and carbon NMR spectrum datas for compound W (201 g/mol) are shown below. Based on Diagram 1 and Diagram 2, draw the structural formula of compound W according to the type of hydrogen and ...
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Assignment of the 13C NMR spectrum of 4'-bromoacetophenone

I was doing a 13C NMR prediction of 4'-bromoacetophenone on chemdraw but I can't figure out why positions 5 and 5' appear further downfield than positions 4 and 4'. I know both Br and the carbonyl ...
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Is this the NMR spectrum of 3-methyl-1-butanol?

It is a $\ce{^1H}$-NMR spectrum and I think the signal near 3,61 ppm is the CH2 group next to the hydroxy group. But which signal is the hydroxy group and which protons are in the multiplet?
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Why would substitution of H with D alter chemical shift?

The $\ce{^{119}Sn}$ chemical shift of the dimeric tin hydride shown below (R=terphenyl) changes on addition of $\ce{D2}$ from a 1:2:1 triplet at $\pu{657.9 ppm}$ (due to coupling between $\ce{Sn}$ and ...
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How do you distinguish ferrocene, acetylferrocene and diacetylferrocene in a NMR spectra? [closed]

I made an experiment where I made a Friedel-Crafts acetylation of ferrocene. Now I would like to know if/how I can distinguish ferrocene, acetylferrocene and diacetylferrocene in a NMR spectra? For my ...
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The type of H-NMR spectra observed for S=PF2H and other inorganic molecules similar to this

I was hoping to learn more about the types of splitting observed in inorganic molecules such as S=PF2H. I am familiar with the typical splitting patterns associated with the study of organic molecules ...
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Why are 13C CP MAS NMR signals sometimes split by N, and absent in dipolar dephasing?

A past paper question on solid state NMR I was looking at asks why, in $^{13}$C CP MAS NMR, carbons directly bonded to nitrogen are "occasionally" split, and why they're usually absent in ...
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How do we explain NMR shielding in filled valence shells?

It is universally recognized that NMR measures the shielding of nuclei from magnetic fields by electrons. The electrons move, producing an eddy current that produces an opposing magnetic field. It is ...
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How to assign overlapping multiplets in 1H NMR spectra?

In the above $\ce{^1H}$ NMR spectrum ($\pu{400 MHz}$, $\ce{CDCl3}$) the methyl, alkene, and $\ce{CCl3CH2}$ protons are fairly easy to assign however, the protons in the cyclohexene ring show overlap ...
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Assigning carbon-13 NMR for ethyl 2-oxo-2H-chromen3-carboxylate

I have a molecule and an NMR spectrum, and I need to assign the NMR peaks to each of the carbons to the molecule: I know that the 14.19 ppm and the 61.94 ppm correspond respectively to the carbon 12 ...
3 votes
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Do the αβ and βα states of homonuclear AX system have same energy?

I was studying nuclear Overhauser effect and came across this diagram$^1$: This diagram shows the energy levels of four possible nuclear spin states of homonuclear AX system. The white/grey boxes ...
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