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
64 views

How does the splitting in this molecule take place?

Consider the following molecule and data: $$ \begin{align} \mathrm{H_a} &= \pu{1.0 ppm} &\quad J_\mathrm{ab} &= \pu{5.0 Hz}\\ \mathrm{H_b} &= \pu{3.0 ppm} &\quad J_\...
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NMR spectroscopy structure determination [closed]

Please help: 1) The 1H NMR spectrum of (S)-glycidyl benzyl ether (300 MHz in CDCl3, with TMS) is shown below, along with expansions of the resonances at 4.6, 3.7, 3.4, 3.2, 2.8, and 2.6 ppm. (20 ...
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Identifying Structure based off 1H-NMR & Mass Spectroscopy Data [closed]

I have almost the whole night trying to identify this structure with no avail as there is always one part that does not fit. The determined formula for this structure was $\ce{C13H17BrO}$ from the $m/...
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Why does ethane not produce proton NMR splitting? [duplicate]

Considering the compound ethane: Why is there only 1 peak in the NMR diagram? I've been told it's because they are in identical chemical environments, but how does that explain why there is only 1 ...
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2answers
127 views

Radiofrequency transmitter in an NMR experiment: Is there an involvement of (electromagnetic) radio wave?

A student in Chemistry StackExchange asked the effect of radio waves on matter, which led to an interesting set of arguments by some users. It was pointed out that in a proton nuclear magnetic ...
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3answers
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What are the effects of radio waves on matter?

Different regions of the electromagnetic spectrum interact differently with matter: Microwave radiation can induce molecular rotation. Infrared radiation can induce molecular vibration. Visible and ...
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0answers
87 views

Why is cis proton coupling larger than trans proton coupling in cyclopropanes?

In Clayden, Greeves, Warren Organic Chemistry Second Edition Page 815, it states: In four- and three-membered rings, cis couplings are larger than trans ... but I did not find an explanation for ...
2
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0answers
72 views

What produces this NMR spectrum? [closed]

I'm having difficulty deciphering this 13C and 1H-NMR spectra. I've tried figuring it out, and have gotten close and am pretty sure it contains a methoxy group attached to a benzyl group, but hit a ...
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H NMR of vanillin detail in Nilered video

The image below is from a Nilered video How to extract Vanillin from Vanilla Sugar, where he displays the H NMR of the final product created: The labels A, F & E make sense to me, but I'm ...
6
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1answer
101 views

Zero-filling Fourier Transform in NMR [duplicate]

I understand zero-filling increases the resolution of an NMR signal in the frequency domain, but I fail to comprehend how. Why do the artifical points appear between the real points in the frequency ...
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EPR or NMR sample that will give narrow lines at 4 K

We have made a crossed coil setup (X and Y transmit/receiving coils) with a SQUID pick up loop along Z. Now we want to see EPR or NMR lines, probably using it in a CW fashion, ie. putting a ramp + ...
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2answers
127 views

Predict the number of peaks in H-1 NMR of sesamolin

Would all of the Hs in an NMR of sesamolin (5-{(1⁠S,3a⁠R,4⁠R,6a⁠R)-4-[(2⁠H-1,3-benzodioxol-5-yl)oxy]tetrahydro-1⁠H,3⁠H-furo[3,4-c]furan-1-yl}-2⁠H-1,3-benzodioxole; shown above) be non-equivalent to ...
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1answer
29 views

NMR of trigonal bipyramidal molecules

I'm slightly confused about NMR. I seem to remember at school that if a molecule is symmetrical in $\ce{^1H}$ NMR, that only one peak would be shown e.g. propane's terminal $\ce{-CH3}$. Consider ...
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NMR for an octahedral complexes sources of peaks

I wanted to ask a question about splitting pattern in NMR. I was given the following information to assign to a Compound C and justify why the splitting patterns are as given: I was confused about ...
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2answers
65 views

Determining identity of unknown compound with NMR data [closed]

I have the following IR spec, C NMR and H NMR data. The boiling points determined for the unknown compound were 116.8 and 119.1°C (two trials). Given the possible compounds, the unknown can be one of: ...
3
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1answer
77 views

Axial Equatorial NMR graph difference

I wanted to ask a question about NMR for Axial and Equatorial molecules. I was asked to describe how to separate the following two product molecules from this reaction: and the answer that my ...
4
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1answer
51 views

Identifying an extra NMR peak in silyl protection reaction

I protected a phenol with the TIPSCl/triethylamine procedure. The product was isolated by column (hexanes/EtOAc) and shows an extra singlet at 1.05 ppm in $\ce{CDCl3}$, integrating to ~10 H. Whatever ...
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2answers
589 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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62 views

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
77 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
48 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
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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 ...
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1answer
164 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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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= ...
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1answer
207 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
106 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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109 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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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
135 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
487 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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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 ...
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2answers
110 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 ...
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1answer
287 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
87 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
280 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 ...
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1answer
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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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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
219 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
127 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
120 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
51 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
97 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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0answers
162 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 ...
4
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1answer
80 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 ...
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1answer
116 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
380 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
27 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
111 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 ...