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.
480
questions
3
votes
1
answer
354
views
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 ...
- 49
5
votes
1
answer
71
views
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 ...
- 51
-3
votes
0
answers
15
views
Are these methylene protons going to be chemically equivalent for this racemic tocopherol derrivative? Are they diasterotopic?
In this molecule, if I am analyzing a racemate not a pure enantiomer would it be the case that the geminal protons on each methylene group (the two CH2 groups) would be chemically equivalent? I would ...
- 1
0
votes
0
answers
42
views
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 ...
- 31
2
votes
1
answer
164
views
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 ...
- 31
2
votes
2
answers
104
views
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 ...
- 21
2
votes
1
answer
59
views
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 ...
- 21
0
votes
2
answers
80
views
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?
- 499
7
votes
1
answer
601
views
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 ...
- 513
1
vote
1
answer
77
views
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 ...
- 333
0
votes
0
answers
32
views
why same-carbon hydrogens produce singlets in NMR [duplicate]
Why doesnt the signal also split here, arent neighbour hydrogens also creating a magnetic effect to other hydrogens?
For example, in CH4, arent different possible spin states that would create ...
- 35
2
votes
0
answers
22
views
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 ...
- 83
0
votes
0
answers
39
views
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 ...
- 1
5
votes
1
answer
67
views
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 ...
- 51
0
votes
0
answers
24
views
Why β-proton of 7-hydroxycoumarin is more deshielded than α-proton?
Umbelliferone (or 7-hydroxycoumarin) has the following signals in the 1H-NMR spectrum:
I don't know if my question makes sense but why the H3 is more shielded than H4 in the α,β-unsaturated lactone? ...
- 83
12
votes
3
answers
665
views
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 ...
- 36.6k
2
votes
1
answer
278
views
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 ...
1
vote
0
answers
35
views
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 ...
- 499
3
votes
0
answers
42
views
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 ...
- 83
0
votes
0
answers
28
views
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 ...
3
votes
0
answers
70
views
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 ...
- 51
1
vote
0
answers
187
views
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 ...
- 1,446
0
votes
0
answers
27
views
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?
1
vote
0
answers
17
views
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 ...
- 139
3
votes
0
answers
201
views
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) ...
- 31
4
votes
0
answers
52
views
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 ...
5
votes
0
answers
143
views
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 ...
- 151
2
votes
1
answer
66
views
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_\...
- 29
3
votes
1
answer
239
views
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 ...
- 163
2
votes
1
answer
206
views
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 ...
- 21
3
votes
1
answer
135
views
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 ...
- 36.6k
6
votes
3
answers
208
views
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 ...
- 165
0
votes
1
answer
79
views
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 $...
- 21
2
votes
0
answers
81
views
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 ...
- 21
3
votes
3
answers
229
views
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. ...
0
votes
0
answers
55
views
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 ...
- 27
0
votes
2
answers
267
views
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 ...
- 881
0
votes
1
answer
144
views
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) ...
- 3
2
votes
1
answer
111
views
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 ...
- 31
0
votes
1
answer
52
views
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?
- 1
2
votes
0
answers
85
views
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 ...
- 21
8
votes
1
answer
669
views
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. ...
- 36.6k
0
votes
0
answers
91
views
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),...
3
votes
1
answer
267
views
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 ...
6
votes
1
answer
198
views
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 ...
- 121
2
votes
0
answers
107
views
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 ...
- 1,183
2
votes
2
answers
160
views
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 ...
user115162
2
votes
2
answers
455
views
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 ...
- 21
4
votes
1
answer
966
views
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 ...
- 101
3
votes
0
answers
82
views
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 ...
- 432