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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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Aromatic NMR in benzyl alcohol [on hold]

Do you know the multiplicity of aromatic hydrogens in benzyl alcohol? In many files on internet I see "5H multiplet" but I want more precision please.
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1answer
35 views

Why does this region fit NMR spectroscopy technique?

I was reading a paper and came across a sentence (highlighted one) about NMR spectroscopy. Several Leishmania Rabs, like Rab1, Rab5a, Rab5b, and Rab7, have been functionally characterized. LdRab5a ...
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1answer
50 views

How is a NMR spectrum obtained?

I am reading about NMR, and from what I'm understanding it should give information on the transition energies in the spectrum of the nuclear spin in a magnetic field. What I don't understand is how ...
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1answer
42 views

4-nitromethylbenzene proton NMR spectrum confusion

I wanted to analyse and suggest the peaks for the NMR spectrum and ran into a problem. I knew that the methyl $\ce{CH3}$ produces a singlet peak with integration $3$ but when I ran into the Benzene ...
2
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1answer
31 views

The C-13 chemical shift of acyl chlorides vs ketones

In lectures, we were taught that ketones and aldehydes tend to have chemical shifts of around 200ppm, while acid derivatives (carboxylic acids esters etc) tend to have values around 160-170 ppm. The ...
4
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1answer
53 views

The carbon-13 NMR for 1,1,1-trichloroethane

I was working the following spectroscopy problem from Clayden 2e that asks us to identify the structure of a compound from information about its carbon-13 NMR peaks. Problem 3.5: The solvent ...
2
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2answers
48 views

NMR: How the relaxation times T1 and T2 depend on the correlation time / amount of molecular tumbling.

Why do nuclei that have a smaller / faster correlation time have a higher / slower T1 / T2? From my understanding: Fast Brownian motion creates a wide range of B.local (local magnetic field created ...
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1answer
21 views

Can nuclear shielding affect relaxation time?

Can nuclear shielding affect the transverse relaxation time, i.e extend the relaxation time the more the nuclei is shielded?
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1answer
67 views

Predict NMR spectra from the Mass Spectrometry

Imagine, you have a tissue and the Mass Spectrometry for it. How would you get the corresponding NMR spectra knowing only the Mass Spec? Is there is a special formula or a well-known technique? I ...
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1answer
43 views

NMR analysis regarding cis-1-isopropyl-3-phenylcyclohexane

I have come across a question in my textbook: The textbook gives this answer: I understand the explanation for the first compound. However, for the second structure, I am not understanding why the 2 ...
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0answers
17 views

NMR sweeping magnetic field

I am currently doing a experiment in the lab which is using a continuous wave NMR, by sweeping the magnetic field, and I am having trouble understanding how the theory works for this type of ...
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0answers
34 views

Q-chem equivalent solvent settings for Gaussian NMR ab inito methods

I'm attempting to use Q-Chem 5.0 to replicate CHESHIRE-esque http://cheshirenmr.info/ ab initio calculations of chemical shift values. Unfortunately Gaussian seems to be the predominant tool in this ...
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How would vicinal coupling of two 1H with intervening 12c nuclei look with a naive Fermi contact model?

Multiple sources I've found talk about vicinal J-coupling between two hydrogen-1 nuclei with two intervening carbon-13 isotopes as in: 1H-13C-13C-1H Which would be (electron spin of covalent bonds ...
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1answer
40 views

Why is the equilibrium constant being calculated differently here?

In my NMR textbook, it says the equilibrium constant for a dynamic process (e.g., A in equilibrium with B) is calculated by the concentration of A divided by the concentration of B. Is this a typo? ...
5
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1answer
125 views

Why are the calculated NMR values on the DFT & GIAO level of cyclopentane-1,3-dione so far off?

I'm trying to simulate the 13C NMR spectrum of cyclopentane-1,3-dione (PubChem CID: 77466; CAS 3859-41-4; ChemSpider ID: 69875; SDBS No: 15258; SMILES: C1CC(=O)CC1=O...
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1answer
61 views

Why does a chiral carbon affect some hydrogen's hydrogen environment?

In the screenshot attached taken from Khan Academy's video (https://www.youtube.com/watch?v=p9B4s0N5yk8&list=PL0pJUwkI0YCZRYrgKqHXZ0XCIu11afbJ8&index=3) the thick pink dot refers to a chiral ...
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1answer
54 views

NMR of phenylethane amine

I did an undergraduate experiment and could use some help in interpreting the $\ce{^1H}$ NMR spectra. This was the task: About $\pu{5-10mg}$ (1-2 drops) distilled amine is weighed in a NMR tube. Put ...
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2answers
55 views

Unique carbons on long carbon chains

If we have a long carbon chain like octane for example, do we determine if a carbon is unique by just looking at the immediate surrounding atoms of each carbon (in this case 3 unique carbons), or do ...
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1answer
159 views

Predicted number of signals in proton NMR spectroscopy

Given the molecule,. I can predict that there will be 4 signals present in the NMR spec. Problem is, the quiz says 5 is the correct answer. My question is, are alkene hydrogen not chemical-shift ...
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1answer
86 views

Why is the residual proton resonance in deuterated benzene a singlet?

In deuterated benzene ($99\%$) the residual protio peak is a singlet at $\pu{7.16 ppm}$. This however doesn't make sense since the protons will be randomly distributed among various benzene molecules. ...
3
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1answer
75 views

1H splitting pattern of benzyl CH2 protons

During my PhD, I prepared the two compounds below (there was actually a slightly longer chain but it's not inherently relevant). When looking at the 1H NMR spectra of these compounds, something ...
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0answers
58 views

Determining Number-Average Molecular Weight from 29Si NMR Data

I have some $^{29}$Si NMR data for a particular poly(siloxane) polymer that we have isolated from a very dilute solution. I can clearly identify tri-substituted (T) and di-substituted (D) species in ...
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103 views

Non-uniform sampling (NUS) in 2D-NMR

The NMR technicians where I work have recently started replacing the standard 2D NMR experiments (COSY, HSQC) with NUS variants (25% sampling). For the uninitiated, the rationale behind the technique ...
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2answers
66 views

Pulsed NMR change in magnetisation vector

When a second, radio frequency magnetic field $\ce{B1}$ is applied perpendicularly to $\ce{B0}$, why does the magnetisation vector M rotate in a direction perpendicular to both $\ce{B1}$ and $\ce{B0}$?...
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0answers
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Where can I find example MS, IR, NMR spectra for teaching molecular spectroscopy?

I am teaching a course on analytical chemistry, and I would like to give my students MS, IR and NMR spectra to practice with. It would be ideal if they could analyze spectra in a more "realistic" way ...
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1answer
36 views

Range of HMBC Coupling

I need to determine the constitution of an organic molecule by several spectra like 1H NMR, 13C NMR, COSY, HMBC ,and HSQC. Is it possible to get a HMBC crosspeak between the marked proton and carbon ...
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1answer
317 views

H-NMR Equivalent Protons and Coupling of Glycerol

I've been searching for explanations to understand why the labeled protons on carbons 1 and 3 are not equivalent in the below figure. Another figure that shows the same results: SDBS confirms the ...
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1answer
59 views

Organic Chemistry Help Please! [closed]

I'm not sure how to even start these two problems. How do you predict the structure of something when its molecular formula isn't provided to you? Also how do you calculate percent purity from this ...
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2answers
212 views

NMR - coupling of chemically equivalent protons

In Klein's Organic Chemistry 3rd Edition page 671, it states This observation, called the n + 1 rule, only applies when all of the neighboring protons are chemically equivalent to each other. ...
4
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1answer
145 views

Why do carboxylic acid derivatives show a more upfield shift than carbonyls in 13C-NMR?

The prototypical 13C NMR shifts of carbonyl carbons is in the range 190–200 ppm, however, carboxylic acid derivatives have a 13C NMR shift in the range 160–180 ppm instead. What structural factors ...
5
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1answer
3k views

What is number of 1H NMR signals for toluene?

I am searching the web for the number of 1H NMR signals of toluene and I find two different results. Some say there are two signals while others say there are four (According to me, it should be 4). ...
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1answer
417 views

Is there a real detection limit in NMR spectroscopy?

From what I've read, my impression is that with a sufficient number of scans etc., one can get spectra from even very dilute samples (S:N ratio ~ $\sqrt{\text{NS}}$). Obviously, this is not always ...
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2answers
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How does the presence of various NMR active nuclei in a compound affect coupling and signal multiplicity?

I am basically wondering how the presence of various NMR active nuclei present in a organic molecules affect the shift values and coupling states normally seen in a molecule lacking these nuclei. ...
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What would be the 19-F decoupled proton NMR of this complex [PtH(PF3)4]-?

The proton is in the equatorial position and the geometry of the complex [PtH(PF3)4]- is trigonal bipyramidal. The NMR is 19-F-decoupled proton NMR. My thoughts were that the proton would couple to ...
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1answer
128 views

What is the identity of the unknown compound using GCMS and NMR?

I've been asked to identify an unknown compound by performing several analytical techniques on it. The compound was a white powder and had a boiling point of 65 degrees celsius. I have the GC mass ...
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1answer
44 views

Are aliphatic amines SABRE amenable?

Hyperpolarization of molecules via the SABRE-SHEATH technique is a fairly new idea. Does anybody know if hyperpolarizing aliphatic nitrogens is possible? The articles I've read mostly use N-...
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5answers
386 views

Utility of proton vs carbon NMR

I've just learnt about both types of NMR, and I haven't ever used NMR in real life, so anything I say may be wrong. The crux of this question is that, in my own opinion, proton NMR gives you more ...
3
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1answer
108 views

Magnetic non-equivalence of acetal protons

I have been using bromoacetaldehyde diethyl acetal recently and noticed something interesting about the 1H NMR. The methylene protons of the ethyl acetal are magnetically non equivalent. You see two ...
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1answer
73 views

Paramagnetic relaxation in 13C nmr

I'm trying to make my 13C{1H} (hydrogen decoupled) nmr more quantitative. From the literature I've noticed that researchers either increase the delay time in the experiment (which I can't do, as it ...
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1answer
86 views

Comparison of chemical shifts among alkanes in NMR spectroscopy

I was reading through the factors influencing chemical shifts in proton NMR. I found the order of chemical shifts in the image above. Why is this order supposed to be as it is? I thought it would be ...
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single crystal LiF solid state nmr

I haven't been able to find any literature on F19 solid state NMR studies of LiF crystals, not even LiF powders. Is there any nmr chemists who is familiar with LiF? Any references are greatly ...
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1answer
149 views

NMR spectrum of 3-hexylthiophene: why is the methyl group not a triplet?

I have an example spectrum, and it shows which peaks correspond to which H, but I don't understand why the spectrum looks like that e.g. I would expect the peak at 0.88 to be a triplet based on the (...
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Assignment of the 13C NMR spectrum of 1-(ferrocenyl)ethanol

The molecule in question has the following structure: The 13C NMR is given below: My assignments are: 23.700 ppm, -CH3 65.569 ppm, CH adjacent to the -OH 66.138/66.183 ppm; 67.924/67.977 ppm, ...
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1answer
144 views

Assignment of the 13C NMR of 2-heptanone

The 13C NMR of 2-heptanone is given below: I understand the assignments of the carbons labelled 7, 6, 4 and 1. My question is: Why is the shift of environment 5 higher than that of 3, despite being ...
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0answers
42 views

Assignment of the NMR of a copper-oxo complex

The 1H NMR of [Cu4OCl10][Me4N]4 in DMSO has the following peaks: 3.31 ppm, medium sized 3.19 ppm, large 2.50 ppm, solvent 1.018 ppm (bump, likely just noise) Why are there two proton environments?...
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1answer
80 views

H1 NMR Spectra of inorganic complex, Cu4OCl6(2-mepy)4

I'm having difficult interpreting the following H1 NMR I have been given for Cu4OCl6(2-mepy)4. The NMR spectra obtained with integration trace beneath. I'm not too sure how to rationalise the 4.5:1 ...
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1answer
46 views

NMR Spectra Oddities

I've noticed that as the chain length of n-alkanes increase, their number of carbon environments tend to 5 peaks, and no more, no less. Why is this? I've looked on multiple NMR (C13 NMR, I might add) ...
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2answers
192 views

Matching the NMR to a compound

I was given a molecule that I had to identify the NMR of. The molecule is 2-methylpent-1-ene (shown below): The correct NMR spectra for this molecule is: My question is, why is this the right ...
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1answer
43 views

Why is it necessary to measure the NMR frequency relative to a standard such as TMS?

The horizontal axis of an NMR spectrum is "chemical shift". A standard environment such as tetramethylsilane is chosen as the zero of chemical shift. The frequency at which resonance occurs for other ...
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1answer
177 views

Directionality of ring current-induced magnetic fields in purines

What would be the directions of ring current-induced magnetic fields in purine-like heterocycles in a ​strong magnetic field? Would be the antiparallel state be a default state for these substances in ...