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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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Identifying this compound based on NMR and GCMS? [on hold]

enter image description here Could you please help me identify my unknown compound based on this NMR and GCMS reading? Thank you!
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2answers
80 views

Proton NMR chemical shift of water peak in different solvents

Why does the water peak appear at different chemical shift values (ppm) in different solvents in proton NMR spectra? For example, the water peak in DMSO-d6 appears at nearly 3.33 ppm, but the same ...
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A broad singlet at 2.27 ppm?

I took the $\mathrm{^{1}H}$-NMR (CDCl3 solvent) of my product, 2,2-dimethoxy acetic acid. Below is what I see: $\delta \: \pu{4.862 ppm}$ (1H), $\delta \: \pu{3.521 ppm}$ (6.78H), $\delta \: \pu{2....
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2answers
68 views

What am I doing incorrectly with this IR/ Mass spec data? [closed]

Hello, I am trying to determine the chemical formula for the following compound. From the IR spec, I see there is a carbonyl present. Moving on to the mass spec, I see an M+ peak of 142, with what ...
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0answers
35 views

Free induction decay in NMR (as stated in Pavia)

There is a statement in a very popular textbook of spectroscopy by Pavia (Chapter 3, Intro. to Spectroscopy), it says "The observed FID is actually an interference signal between the radiofrequency ...
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1answer
33 views

Meaning of polarization pulse in microwave (rotational) spectroscopy

In the recent rotational spectroscopy literature, "microwave polarization pulse" is often used in conjuction with pulsed Fourier transform microwave spectroscopy (Google Scholar). Sometimes the pulse ...
0
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1answer
64 views

What defines a proton as “labile” in NMR? [closed]

What makes some protons labile and others not? For example the OH and NH2 protons get exchanged but CH ones don't. When we use the D2O test, we say the labile protons get exchanged for D so their ...
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0answers
39 views

Why ¹H–¹⁴N coupling is not observed in ¹H NMR

Since the nuclear spin value of $\ce{^{14}N}$ is $I = 1$, we should expect a coupling between $\ce{^1H}$ and $\ce{^{14}N}$. Hence, the proton peak in a primary amine $(\ce{-NH2})$ should split in a ...
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NMR spectrum of 1-phenyln ethanol

My question is about the the peaks in an NMR spectrum of the molecule 1-phenyl ethanol. They have already given the answer for the benzene ring attached. The CH3 is easy to be found at chemical shift= ...
5
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1answer
162 views

How to report a triplet of septets in NMR tabulation?

Does anyone know the proper format to report an iso-butyl group, eg. $\ce{R-CH2-C\color{red}{H}(CH3)2}$, in $\ce{^1H}$ NMR tabulation? The proton in red should be a triplet of septets, so I've written:...
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1answer
85 views

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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59 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. ...
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47 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 ...
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3answers
72 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 ...
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2answers
144 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 ...
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0answers
29 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
81 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
215 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, ...
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1answer
59 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
183 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 ...
5
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1answer
70 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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23 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 ...
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1answer
167 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
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1answer
78 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 ...
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1answer
91 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 ...
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1answer
50 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 ...
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1answer
50 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
81 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
112 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 ...
3
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1answer
53 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
83 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 ...
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2answers
244 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
23 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
97 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
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1answer
57 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 ...
3
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1answer
54 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
64 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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1answer
41 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? ...
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1answer
135 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
90 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
68 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
78 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
362 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
123 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. ...
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1answer
105 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
148 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
90 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
80 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 ...
4
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1answer
49 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
514 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 ...