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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The carbon-13 chemical shift of acyl chlorides vs ketones

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

Is it possible to estimate the abundance of conformers from J values?

I have a system of two disubstituted cyclohexanes and I want to estimate the abundance/ratio of the two based on the J values and if possible, roughly estimate the difference in free energy. To get ...
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63 views

Explanation of Specific Chemical Shifts on an H-NMR Spectrum

Recently, I've been looking into chemical shifts on H-NMR Spectrums and I came across a graph I didn't quite understand... As you can see from the spectrum attached, the signal emitted from the ...
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519 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 ...
5
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1answer
149 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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128 views

NMR in pyridine no meta splitting

Consider the NMR of Brominated Pyridine shown below: When I looked at the NMR data, I was confused because I thought that H2 would also be split in the meta position by H6 but the data says that this ...
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95 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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2k views

How to calculate the spin of atomic nuclei?

I have recently been learning about nuclear magnetic resonance spectroscopy. It is mentioned that the spin of the $^{1}$H nucleus is $\frac{1}{2}\ $and the spin of the $^{2}$H nucleus is $1$. This ...
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877 views

Why does diamagnetic current induce a downfield while the paramagnetic current induces an upfield shift?

I know that aromatic rings exhibit diamagnetic ring currents which causes the protons outside the ring to go downfield in H-NMR. Antiaromatic compounds exhibit paramagnetic ring currents which have ...
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1k views

Identifying the structure of an amino acid from NMR spectra

I have the 1H, 13C, and DEPT spectra of an unknown compound, listed in text form below, but I have also attached original images of the spectra. I know that it is an amino acid that has a cyclic ...
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50 views

How to make standard sample for NMR signal-to-noise ratio

I want to make a sample for proton NMR signal-to-noise-ratio measurement. It is conventional to use 1% ethylbenzene in d-chloroform, as specified here. I have two questions: What is meant exactly, by ...
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38 views

Why is the 2-bond (Sn-H) coupling constant larger than the 3-bond Sn-H coupling constant for tetraethyltin?

I was looking at the NMR spectrum of tetraethyltin [$\ce{Sn(CH2CH3)4}$], and found that the $\ce{Sn-H}$ coupling constant between $\ce{Sn}$ and $\ce{CH2}$ is larger than that between $\ce{Sn}$ and $\...
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48 views

Which atoms in indole possess the greatest amount of electron density?

Presumably the amine acts as an electron donor, but that would suggest extra electron density of the adjacent carbons, making them more shield, which isn't seen in the results in the image below. ...
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16 views

Why are 13C CP MAS NMR signals sometimes split by N, and absent in dipolar dephasing?

A past paper question on solid state NMR I was looking at asks why, in $^{13}$C CP MAS NMR, carbons directly bonded to nitrogen are "occasionally" split, and why they're usually absent in ...
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35 views

Why would T1 relaxation time change ~20 fold between solvents for the same substance?

I have a simple, completely conjugated pyridinium salt with MW of ~300 g/mol. The molecule consists of regular non-labeled atoms (only C, H, N). If the 1H T1 relaxation time for this molecule is ...
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46 views

Challenges Associated with Earth's field NMR

The ACS recently hosted a virtual conference and there was an interesting talk on NMR experiments using the Earth's magnetic field. What surprised me was the number of molecules studied with Earth's ...
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41 views

Distinguishing between different geometries of bromochlorobis(triphenylphosphine)platinum(II) using ¹⁹⁵Pt NMR

Question The question off which I am basing my question assumes that $\ce{[PtClBr(PPh3)2]}$ can exist in either the square-planar or tetrahedral geometry. If one would use $\ce{^{195}Pt}$ NMR ...
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33 views

Chemical shift difference methyl groups in 4-hydroxy-2,5-dimethyl-3-hexanone

Can someone explain why the NMR Spectrum of 4-hydroxy-2,5-dimethyl-3-hexanone shows a chemical shift difference for the methyl groups at the end? Why aren't the other carbons have a difference? Below ...
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136 views

Why does Larmor precession occur in NMR?

Larmor precession is the phenomenon that in NMR the spin (and by default also the magnetic dipole moment) of protons does not line up with the applied magnetic field but rather precesses around this ...
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982 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 ...
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97 views

Find NMR equivalent atoms

I'm trying to find a program/algorithm/API that can find the equivalent atoms in a molecule when given a molecule (knowing the complete geometry with x, y and z coordinates, and bonds between the ...
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247 views

Magnetic anisotropy of triple bonds

Is the rule for shielding/deshielding areas in NMR bond dependent? The acetylene C triple bond C has deshielding zone perpendicular to the triple bond. Will the same deshielding zone hold true for C ...
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91 views

Why does the addition of heavy water cause OH and NH peaks in NMR spectra to disappear?

When $\ce{D2O}$ is added to a sample, the OH and NH peaks in a $\ce{^1H}$ NMR spectrum disappear. This is the basis of (for example) the $\ce{D2O}$ shake test, and is also the reason why peptide/...
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23 views

How do we explain NMR shielding in filled valence shells?

It is universally recognized that NMR measures the shielding of nuclei from magnetic fields by electrons. The electrons move, producing an eddy current that produces an opposing magnetic field. It is ...
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36 views

Origin of the NMR shielding

In a paramgnetic material the induced dipole moment of atoms or (molecules) of the material aligns with the external field. I can understand this by Zeeman splitting. A term symbol splits into states ...
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44 views

$j$-$j$ coupling interaction in Magnetic Resonance Spectroscopy

I am studying Magnetic Resonance Spectroscopy and I have some difficulties in understanding the j-j coupling interaction. What does actually happen from the physical point of view to the electronic ...
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156 views

H NMR signals in 1,4-dichlorobutane spectrum

I have come across H NMR spectrum of 1,4-dichlorobutane and I have noticed that signals there are different to what I would intuitively expect. Instead two triplets there are two multiplets of more ...
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81 views

How far does the delocalisation (resonance) effects for substituents extend for a conjugated system?

Let's say we have a conjugated system like this one: Now, the delocalisation of the benzene electrons with the nitrate system means that the ortho, and para positions on the immediate benzene ring ...
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34 views

NMR Coupling in an aromatic system via π system

I was presented today with the following molecule: and asked the splitting pattern of $\ce{H_a}$ given that up to $\mathrm{^3J}$ and $\mathrm{^4J}$ coupling is allowed. I thought that $\ce{H_a}$ ...
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222 views

which oxygen atom make intramolecular hydrogen bond in salicyclic acid?

When I googled about intramolecular hydrogen bonding in Salicylic acid, I found that there are two type of hydrogen bonding. Which one is more appropriate? And another question, if there ARE two ...
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52 views

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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132 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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80 views

Single crystal LiF solid state NMR

I haven't been able to find any literature on $\ce{^{19}F}$ solid state NMR studies of $\ce{LiF}$ crystals, not even $\ce{LiF}$ powders. Is there any NMR chemists who is familiar with $\ce{LiF}?$ Any ...
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1k views

C-13 NMR: Why are sp hybridized carbon atoms less shielded than sp3 hybridized carbon atoms but more shielded than sp2 carbon atoms?

For example, when you look at hex-1-en-5-yne, you'll find out that the terminal carbon with the triple bond has a reading of 69.7 ppm and the internal carbon with the triple bond has a reading of 86.1 ...
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59 views

H1 NMR integrations

I know this may be a bit of a dull question considering the integration on hydrogen NMR are usually quite precise but I was wondering If integrations in a linear depsipeptide compound could be thrown ...
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1k views

What causes the deshielding in carbon - carbon bonds?

I thought of this question while reading through a chapter on Carbon 13 NMR. It's easy to see that in a bond with two different atoms, such as in a bond involving $ \mathrm C$ and $\mathrm O$, that ...
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85 views

19F MAS NMR chemical shift tensor and the crystal structure

$\ce{^{19}F}$ MAS NMR is measured on fluorine-doped $\ce{TiO2}$. $\ce{F}$ is to substitute $\ce{O}$ and the crystal structure is anatase, which has a tetragonal crystal system with a space group $\ce{...
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29 views

Assigning carbon-13 NMR for ethyl 2-oxo-2H-chromen3-carboxylate

I have a molecule and an NMR spectrum, and I need to assign the NMR peaks to each of the carbons to the molecule: I know that the 14.19 ppm and the 61.94 ppm correspond respectively to the carbon 12 ...
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63 views

Splitting of ethyl ester proton NMR

I synthesised a dihydropyridine molecule today and recieved my NMR. I am wondering where the complex splitting for the 7 and 22 protons is coming from. My spectrum: 1.26ppm, triplet, 6H 2.33ppm, ...
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200 views

Proton NMR of tert-amyl alcohol

I just started learning about proton NMR. According to Molbase, the HNMR data for tert-amyl alcohol (2-methylbutan-1-ol) shows four kinds of protons at 0.9 ppm, 1.24 ppm, 1.44, and 3.65 ppm. However, ...
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27 views

HNMR spectroscopy mono-carboxylated acid

During lab, I have done following reaction: I did HNMR of the product, to be certain if the product really was formed. The HNMR gave following results: And looked like this: So my question is: has ...
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36 views

What is the best way to go about matching proton-NMR spectra to molecules?

I've attatched an example question. I have already solved this one, I'm wondering about what, in your experience, is the most time-efficient way of approaching a question like this one. I can solve ...
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266 views

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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61 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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53 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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72 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 ...
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200 views

Assignment of the 13C NMR spectrum of 1-(ferrocenyl)ethanol

The molecule in question has the following structure: (source: sigmaaldrich.com) 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;...
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104 views

1H NMR impurity peaks don't align across samples

I have a series of four 1H NMR spectra for a polymer I'm synthesizing under different reaction conditions. However, the acetone and chloroform peaks are shifted relative to each other across the ...
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206 views

How to predict the correct splitting pattern in a NMR spectrum

If I were to do a simulation and obtain all the chemical shifts and coupling constants between the different atoms, how would I then predict the NMR spectrum with coupling. Without coupling, I just ...
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708 views

How to assign peaks to mannose using H-NMR and COSY?

I did a H-NMR experiment with D-mannose in deuterated DMSO. I have difficulty assigning the peaks. I know doublet a is the anomeric centre C1 and that triplet f is the OH attached to C6. Doublets b,c,...