Nuclear Magnetic Resonance. This tag relates to NMR spectroscopy, the experimental technique of measuring the resonance and thus deducing the molecular structure of the given compound.

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Propose a structure base on the molecular formula and 1H NMR spectrum [closed]

The molecular formula is C9H8O4. I came up with the structure known as caffeic acid but it does not match the some of the peaks. I know that there has to be a benzene ring along with two double ...
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1answer
97 views

Interchange of axial and equatorial groups in Me2NPF4

The $\ce{^{31}P}$ NMR spectrum of $\ce{Me2NPF4}$ when recorded at room temperature consists of a quintet with intensities $1:4:6:4:1$. However, at $-100~\mathrm{^\circ C}$, the spectrum is as shown ...
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57 views

What does radiofrequency really do in NMR & MRI?

In NMR, the protons’ frequencies are affected by the magnet which makes them precess around its magnetic field so now all protons will have different frequencies according to their environment ...
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2answers
119 views

Why only one peak is observed in NMR spectrum of H2?

Assuming a downward magnetic field is applied and the nuclear spin of two equivalent protons in $\ce{H2}$ are all in ground state $\downarrow\downarrow$ initially. Would the required energy of one of ...
5
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1answer
52 views

Diastereoisomer of quinic acid and its proton NMR?

The question is such: Quinic acid, A, has the gross structure shown below: (i) Draw all the possible diastereoisomers of A and indicate which are chiral. (ii) Quinic acid is optically ...
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1answer
55 views

How to distinguish diastereomers of unsaturated ketones by NMR?

I am synthesising a natural product that contains an α-methylated α,β-unsaturated ketone (see image below). The natural product’s stereochemistry is an (E) configured double bond. I ...
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1answer
61 views

Interpretation of 1H-NMR spectra for Z-ochtodenol

I'm struggling to understand the 1H-NMR data for this compound. I managed to find the compound using the data I had, but at the end I can't assign the peaks properly. My confusions are: ...
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1answer
28 views

NMR coupling pattern for hydrocarbon

What does the 1H NMR spectroscopy coupling pattern look like for the hydrogen attached to the carbon that the blue arrow is pointing to? There is a $\ce{CH2}$ attached to ether side of the carbon, ...
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24 views

Coupling patter for a methyl-butyl ether [duplicate]

What would the high resolution H-NMR spectroscopy coupling pattern look like for the hydrogen attached to the carbon the arrow is pointing at? I am confused because there is a CH2 connected to either ...
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0answers
37 views

Explanation for these 1H NMR spectra?

In CDCl3 solution, the different diastereoisomers of 3-amino-2-butanol have different 1H spectra: for one diastereomer, the coupling constant between H atoms on C2 and C3 is 6 Hz, for the other it is ...
5
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1answer
67 views

Why are protons in the same position in 1-chloro-4-nitrobenzene magnetically different?

Protons in ortho positions towards the nitro group are said to be magnetically different, even though they're chemically equivalent. Same goes for protons ortho towards the chlorine. Why is that so?
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1answer
42 views

Deuterated solvents vs. regular solvents

Working on dissolving aspartame and i was wondering if it dissolves well in methanol will this mean that it dissolves well in deuterated methanol ?
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26 views

How to isolate and determine an unknown molecule in a known heterogeneous mixture using HNMR

I am currently working on an assignment as part of my second year lab course. Essentially I have to determine the unknown molecule which is present at 5-15 wt% in 1 gram of Aspartame. I am planning ...
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1answer
72 views

Proton-decoupled phosphorus spectrum of a ruthenium complex

>Regarding the complex $\ce{[RuH2(CO)(PPh3)3]}$ There are three possible ochtahederal stereochemical configurations, a) Draw these isomers indicating which, if any, are chiral and identify ...
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1answer
47 views

How does one calculate chemical shift in a gauge independent manner?

The literature on ab initio calculations of chemical shift in NMR experiments usually provide Lamb's and Ramsey's formulae as the solution. Yet the expressions explicitly depend on vector potential ...
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1answer
135 views

How many peaks would there be in H1 NMR of ethene?

Would there be 2 peaks? Since the bonds can't rotate. Likewise, how many peaks would there be in trans-but-2-ene and cis-but-2-ene?
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2answers
93 views

Shifting of axial and equatorial protons

I know this NMR represents cyclohexanol and I have figured out what each peak represents. If the 3 peaks at 1.9, 1.7,1.5 all represent equatorial protons as they are shifted downfield compared to the ...
3
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1answer
83 views

NMR analysis problem

I've been given this NMR along with the IR and Mass Spec and assigned the task of figuring out the unknown compound. I know that it is cyclohexanol and by analysing the NMR I know that the peak at ...
2
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1answer
107 views

Why does DMF (dimethylformamide) have 3 peaks in its 1-H spectrum?

I get that the carbons can't rotate around the nitrogen due to its partial double bond character, but how does this result in the hydrogens being in different environments? As such would this mean all ...
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NMR: Estimate rate of coalescence when coalescing signals are multiplets

The coalescence rate on a 300 MHz spectrometer can be found from $$k_C \approx 2.22 \cdot \Delta \delta * 300 $$ The difference in chemical shift is easy to find when only singlets coalesce, but ...
2
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1answer
61 views

Identifying spin system for ethyl butanoate

I am to identify the spin system of ethyl butanoate, but I am confused as to how I should start. Chemically equivalent and not magnetically equivalent: $\ce{AA'A''}$ or $\ce{BB'B''B'''}$, etc ...
2
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2answers
87 views

H NMR of 4-chloroacetophenone

For the H NMR of the compound I am wondering why peak (A) is the farthest out of all of them? I think that it is due to the electro negativity of oxygen. Am I correct? If so, why would the presence of ...
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1answer
68 views

Is there a consensus how to report coupling patterns greater than quartets?

When analysing NMR spectra, every student at one time during their chemistry studies learns about vicinal coupling and that it produces the characteristic signal shapes of proton spectra. The ...
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23 views

How to control the purity and quality of fatty acids or their CoA thioesters?

Background: We are looking into getting a series of cis-mono-unsaturated very-long-chain (C20-C32) fatty acids (with different, specific double-bond positions) — and/or the corresponding acyl-Coenzyme ...
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2answers
159 views

Why do triple bonds have a low NMR value?

Double bonds has a positive shift compared to single bonds. It seems like that there would be a trend but then the triple bond negatively shifts, despite having great electron density similar to the ...
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1answer
99 views

Distinguishing pentanol isomers in 13C DEPT NMR spectroscopy

Pentanol has eight isomers as shown below. The circles represent carbon atoms that I think are equivalent. Below there are eight DEPT-spectra that should represent these eight substances. As you ...
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1answer
74 views

What kind of structure could give you a HNMR spectrum consisting of a singlet integrating to 5 protons?

I'm racking my brains for this and I can't seem to think of any possible structures. Should note that this is homework, and a clean spectrum was given to me with the integrations filled in. I just ...
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2answers
331 views

1H (proton) NMR spectra for alkanes

I do not fully understand the idea of coupling and why chemically equivalent hydrogens do not couple. I wanted to work with the alkanes, so let's take propane first: There would be a triplet ...
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1answer
65 views

Determination of brominated aromatics by 13C and 1H NMR spectroscopy

How can I identify 4-bromoazobenzene, 4-bromoazoxybenzene, and 4,4’-dibromo-$\ce{N,N}$’-diphenylhydrazine products using $^1\ce{H}$ and $^{13}\ce{C}$ NMR? I’m really confused by the general shape of ...
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1answer
177 views

Deducing compounds from spectroscopic data for isomers of formula C4H8O

Here's the problem: I've already know the 3600 cm$^{-1}$ line indicates the $\ce{-OH}$ group and the 1640 cm$^{-1}$ line indicates the C double-bond C alkene. From the $^{13}$C NMR data: the two ...
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1answer
162 views

Calculated 13C NMR Shifts of brominated Carbons

Since I calculate NMR spectra for a while by simply using one of recommendations by CHEmical SHIft REpository: mPW1PW91/6-311+G(2d,p)-SCRF//B3LYP/6-31+G(d,p) ...
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1answer
47 views

Proton NMR Ratios [closed]

Question: Analysis by NMR during a reaction can be difficult because of the number of molecules present. If a small aliquot of the reaction mixture in this experiment were taken and added to ...
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1answer
194 views

Strange 1H-NMR signals/signal ratio

Fedorov et al. assign the $^1$H-NMR ($\ce{CDCl3}$) chemical shifts of the $\ce{CH2}$ group in 2-(bromomethyl)phenylboronic acid to three singlets at $4.75$, $5.09$ and $5.15~\ce{ppm}$ in a ratio of ...
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1answer
117 views

Determining Molecule Based on Proton NMR (HNMR)

Based on the NMR data, I have determined that the molecule must be 1-phenoxy-2-propanone, however I may be wrong because given the proton NMR, there are only 4 unique carbon environments, however in ...
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1answer
105 views

Why is an alcohol proton so shielded?

Considering how electronegative oxygen is, why is the chemical shift of alcohol protons (1H-NMR) not so high? The chemical shifts of the protons on 3-propanol are about 1.20 for the carbon-1 ...
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1answer
38 views

Are there any free phosphorus-31 NMR spectral libraries?

I know that there are some sites like Sigma Aldrich and AIST for $\ce{^1H}$ NMR and $\ce{^13C}$ NMR, but was wondering if there were any free sites to compare $\ce{^31P}$ NMR spectra?
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How to compute the NMR shift in Gaussian09 for only one specific atom in a bigger unit cell?

I am trying to compute the NMR shift for a specific atom in the middle of the surrounding crystal unit cell (1 surrounding anion sphere and 1 cation sphere) in Gaussian09. I only need the chemical ...
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1answer
114 views

hydrogen environments of benzophenone

The hydrogen in $\ce{C4}$, $\ce{C6}$, $\ce{C10}$ and $\ce{C8}$ belong to same hydrogen environment. The hydrogen in $\ce{C3}$, $\ce{C1}$, $\ce{C11}$ and $\ce{C13}$ belong to the another hydrogen ...
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Why does the transverse magnetization in Fourier Transform NMR consist of Ix+iIy ($\hat{I}_x+i\hat{I}_y$)?

More specifically, the expression for the average expectation value of the transverse magnetization has the following form: $$M^+(t)=N\gamma \hbar \text{Tr}(\hat{\sigma}(t)\hat{F}^+)$$ with ...
7
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1answer
133 views

What does the 129Xe NMR spectrum of XeOF4 look like?

What will the $\ce{^129Xe}$ NMR spectrum of $\ce{XeOF4}$ look like? I know that its electron pair geometry is octahedral, and the molecular pair geometry is square pyramidal. I believe that the ...
5
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1answer
71 views

How can I link the data to what I know as correct?

I am currently struggling with an assignment question regarding structural determination using both $\ce{^1H}$ and $\ce{^{13}C}$ NMR data. The first thing I have done is calculate my double bond ...
3
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1answer
73 views

Why are signals of carbon and hydrogen atoms (in NMR spectra) split by coupling to 19F?

Why signals of carbon and hydrogen atoms (in NMR spectra) are split by coupling to $\ce{^{19}F}$? Some spectra books only states that $\ce{^{19}F}$ (natural abundance 100%) has a spin quantum ...
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1answer
2k views

Are the circled hydrogens homotopic, enantiotopic, diastereotopic or unrelated?

I'm very confused. According to the answer key, the circled hydrogens are diastereotopic. I thought they were enantiotopic. My thought process is the following. They aren't homotopic because ...
2
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1answer
38 views

Proton attached to N or O in HNMR spectroscopy [duplicate]

I was wondering why a hydrogen attached to a nitrogen or oxygen is not able to couple with p+ on adjacent carbon atoms and hence why it always appeats as a singlet in HNMR spectroscopy?
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1answer
84 views

Multiquantum coherences in NMR spectra

Why are multi-quantum coherences unobservable in regular NMR experiments ? This is relevent to the DQ-filter experiment which exploits this property.
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119 views

[BrF6]- and its 19F NMR

$\ce{[BrF6]-}$ is an octahedral molecule. I think it would have only one fluorine environment due to the rotational symmetry. $\ce{Br}$ has nuclear spin $I=3/2$ and therefore is unlikely to cause ...
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93 views

HNMR identification problem

Heyo, this a repost because my previous post's format was a bit mediocore and hence I though it would be just better to redo the post again. I have been trying to solve this NMR question for about 4 ...
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1answer
284 views

Spins spin coupling on proton NMR for an aldehyde?

On a proton NMR, does the hydrogen in the CHO group cause coupling, or get coupled itself? Specifically, I a considering 2-methylpropanal. I cannot decide whether the H in the aldehyde group would be ...
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43 views

The nuclear Overhauser effect

I am having some trouble with understanding the NOE. The carbon NMR spectra can't be integrated, because the protons attached to the carbon atoms will make primary carbon atom relaxation faster than ...
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196 views

What happens to chemical shifts of protons close to aromatic systems in ¹H-NMR?

I have two questions regarding chemical shifts on aromatic systems. First, what does being near an aromatic system do to protons? If we look at the spectra of 1-napthalenemethanol and then ...