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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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1answer
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What could cause a peak to split into 2 resonances as temperature increases in NMR spectroscopy

I understand that some peaks may coalesce upon an increase in temperature due to an increase in free rotation, this does occur with some peaks in my data. Why might you see a peak split into two other ...
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22 views

How do I solve this question? [closed]

Analyse the graph and predict the compound
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16 views

Predict the aldol condenation product given IR and H-NMR spectra

An aldol condensation product would have a ketone and at least one alkene in the form of R1-C(=O)-C(R2)=C(R3)-R4 H-NMR: 7.09ppm 1H doublet, 7.42ppm 3H triplet, 7.64ppm 2H quartet, 7.75ppm 1H doublet. ...
4
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38 views

Internal standard with low T1 for NMR quantification of ammonia

I am trying to quantify low levels of ammonia with NMR. The good news is that ammonia has a very low T1 (<0.5) which shortens d1 a lot. However, I cannot find any internal standard with a T1 that ...
2
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3answers
54 views

Comparison of chemical shift of methyl group attached to alcohol and carboxylic acid

I understand that hydrogens can be deshielded by electron-withdrawing groups, and the more powerful the group, the greater the chemical shift. However, I ran into a problem when qualitatively compare ...
0
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2answers
71 views

Protons on aromatic rings in NMR

Recently, I have started to learn about nuclear magnetic resonance (NMR) in school and something which I cannot seem to reconcile is the fact that all aromatic protons on any substituted benzene ring ...
0
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0answers
26 views

NMR Prediction for compounds at variable pH values

Like the title says, I'm looking for any software package that may be able to simulate a variety of NMR at a variety of different pHs. The majority of the software programs that I've found do not have ...
0
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2answers
62 views

How to identify the structure of an organic acid based on its reactivity, mass and NMR spectrum?

Taken from OCR A Chemistry Unified Chemistry Sample Paper. Information about a monobasic organic acid D is shown below. D reacts by both electrophilic substitution and electrophilic ...
6
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1answer
166 views

Why does the 31P{1H} NMR spectrum of cis-[Mo(CO)2(dppe)2] show two signals?

I've tried searching for literature references that explain this, finding only a single reference which refers to the two signals as originating from phosphine environments cis/trans to carbonyls, ...
0
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1answer
49 views

Differences between ¹³C-decoupled NMR experiment vs a ¹³C-coupled

How does the acquisition time changes between $\ce{^{13}C}$–decoupled NMR experiment vs a $\ce{^{13}C}$–coupled? Would the acquisition time be longer if a decoupling of the protons (H) is carried out?...
6
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1answer
111 views

Why do aromatic compounds have an upfield shift upon coordination to metals?

Why do aromatic compounds have an upfield shift upon coordination to metals e.g. ferrocene? The 1H NMR shows a single environment at ~4.1 ppm. This is in contrast to the usual aromatic shift of ...
4
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1answer
56 views

Chemical shifts of OH protons

The chemical shift of a proton is an indication of the amount of shielding it receives from the electron density on it or other magnetic anisotropy effects present in the molecule. For the protons of ...
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0answers
20 views

Why do identical protons not couple with each other in 1H NMR? [duplicate]

So basically I'm wondering why the different protons in ...let's say trans-stilbene do not couple with each other. I'm aware of the fact that they are chemically and magnetically equivalent. They ...
2
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1answer
132 views

Polymer Chemistry NMR question [closed]

I am extremely new to both polymer chemistry and NMR. I am struggling with the following question: A proton NMR is used to attempt to quantify the molecular weight of a poly(ethylene oxide) molecule ...
4
votes
1answer
68 views

Why does the proton NMR of ferrocenecarboxaldehyde appear to be four singlets?

One singlet stems from the aldehyde H, and another from the Cp ring with 5 hydrogens attached. However, the ring with the aldehyde group attached has hydrogens in two chemical environments which are ...
0
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1answer
81 views

Which organic compound's NMR and IR are these? Can't find out. (Data available: Melting Point ~ 116 °C)

Which organic compound's NMR and IR are these? I have figured out that the compound is a 1,4 substituted benzene. And the substituents are probably not -COOH and -OH from the spectroscopy. Kindly help ...
1
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1answer
49 views

How to write correct NMR integrals in a formula?

for my masterthesis I want to include the Equation how I calculate my conversion in a polymer reaction. It is pretty easy, but I still want to write it down. Basicly the equation is: (Integral A ...
1
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1answer
47 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 ...
5
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1answer
55 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 ...
3
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0answers
84 views

1-Methyl-4-nitrobenzene 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
votes
1answer
37 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
votes
1answer
69 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
124 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
91 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 ...
3
votes
1answer
51 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 ...
2
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1answer
41 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 ...
2
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0answers
52 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 ...
0
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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
129 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...
2
votes
1answer
79 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 ...
1
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1answer
57 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 ...
0
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2answers
66 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 ...
1
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1answer
280 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 ...
5
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1answer
104 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
93 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
118 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 ...
4
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2answers
81 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
68 views

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 ...
3
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1answer
42 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
420 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
63 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 ...
5
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2answers
233 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
322 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
5k 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). ...
12
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1answer
542 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 ...
3
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2answers
119 views

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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0answers
42 views

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 ...
0
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1answer
148 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 ...
4
votes
1answer
47 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-...