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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Why does peak decoupling occur in H-NMR spectra?

For example, when we analyze the conversion of some chemical compound, certain characteristic areas tend to decrease (ok). However, why can a peak (i.e., one peak) generate smaller peaks (i.e., more ...
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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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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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Why does sensitivity of nmr spectrum improve with increased magnetic field strength

I am struggling to find an equation that illustrates this and a qualitative explanation to go along with it. I presume that the noise remains at the same intensity and somehow the intensity of the ...
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On the angle subtended between the angular momentum vector and the applied field for a single spin

According to Dr James Keeler of Cambridge University in one of his lectures at Queensland University, the angle theta can be any angle, but I struggle to see how this is true. There are only a certain ...
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On the origin of spin-lattice relaxation

According to P.J. Hore in the Oxford Chemistry Primer "Nuclear Magnetic Resonance" p57, 'the dipolar coupling, modulated by molecular motions, causes nuclear spins to experience time-dependent local ...
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NMR magnetically equivalent protons for a 1,4-disubstituted benzene ring

Below I have drawn a molecule with random substituents $\ce{X}$ and $\ce{Y}$: If the distances from $\ce{H_b}$ and $\ce{H_a}$ to $\ce{H_d}$ are considered, they are different - $\ce{H_b}$ is 5 bonds ...
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Interpretation of Carbon-13 NMR Spectra for Chemically Similar Carbon Atoms

I am analyzing the Carbon-13 NMR data from a reaction I will be modifying. There is not NMR data available for the specific compound I am attempting to synthesize; however, the compound I am ...
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NMR splitting of protons in a ring

I was presented with the following compound and asked to comment on the splitting of the proton $\ce{H_a}$ in $\ce{^1H}$ NMR. The question presented today was: What is the chemical shift (below) ...
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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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NMR of a bridging Methyl complex

I was provided with the following structure of an inorganic metal complex: And asked to give information on its NMR spectrum shown below The highfield signal is caused by a singlet with Platinum ($I ...
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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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How can the formula of WD-40 remain a trade secret?

Wikipedia says WD-40's formula is a trade secret How can it remain a secret today? Can't mass spectrometers, NMR and other equipment be used to determine the structure of the compounds that go ...
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Why does the nitrile carbon experience more shielding than a carbonyl carbon in CNMR?

In organic chemistry lecture, we were given a chart of approximate signal shift ranges for different carbon types in CNMR spectra. carbonyl carbons (C=O) have a range of about 155-210 ppm, but the ...
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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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What do X-ray diffraction and NMR tell about the Proteins? [closed]

I have gone through a simple idea that proteins have different conformations; it is a dynamic system. Moreover, whenever we do ensemble experiments, so we get an average picture. There are some ...
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Why do the NMR peaks shift when H+ concentration and temperature are varied on the reversible hydrolysis of pyruvic acid to 2,2-dihydroxypropionate? [closed]

We performed two experiments. Each of the peaks are referring to the methyl peaks in both reactant and product of the hydrolysis reaction. We varied $\ce{H+}$ concentration of the reaction and the ...
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AX Spin system ordering

I would like to ask a question about the ordering of the $\ce{X}$ spins on the right hand side of an $\ce{AX2}$ energy diagram. I was given the diagram here below: and asked to evaluate why this ...
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Definition of NMR peak

In NMR a spectrum consists of noise and peaks. While steps, such as repeated scans or smoothing of the spectra can reduce noise some still remains. As such one step usually taken is to bin the data so ...
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Determining structure from C-NMR spectrum, is my answer correct?

Determine the structure of the compound whose spectral data is given below and explain your reasoning (5 marks for structure, 15 marks for reasoning). The peak at 7.27 ppm does not belong to the ...
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Identify the structure of the compound (C3H5NO) given its NMR chemical shifts

I am trying to figure out the structure of the compound $\ce{C3H5NO}$ given just the following data from the 1H NMR spectrum: $\delta 5.8 ~ \text{(singlet, 1H)}; \delta 6.2 ~ \text{(triplet, 2H)}; ...
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H-NMR with 10H integration?

I have the following two spectra (IR and 1H-NMR) see below. The chemical formula is: C16H16O2 Thus DBE = 9 My approach: From the IR, I can see that there's no broad peak around 2500-3300, thus I ...
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Am I using these spectra to identify the compound correctly?

What is the structure of the molecule whose data is shown below? Explain your answer [...] EI mass spectrum: The highest peak observed is $m/z$ 210 and its abundance is low. The only other significant ...
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How to recast Henderson–Hasselbalch when fitting data on a chemical shift vs. pH graph for NMR

I've just been getting into organic and been reading about H-H related to $\mathrm{NMR}$. I've been seeing articles state how recasting of H-H is necessary and want to know how equations like below ...
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Determine structure from NMR

So I've come across this lovely spectrum of a compund where only its chemical formula is given with C5H9NO. I have made the pictures of the spectrum available below. obviously there is some pretty ...
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How do I figure out how many hydrogens my compound actually has using a mass and NMR spectrum?

Question 3: It said $m/z = 122,$ and $m/z = 124$ is in a $3:1$ ratio, so I figured that meant that chlorine is present. Then I thought $m/z$ was the actual compound's molecular mass. So I used ...
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Determining number of unique hydrogens in lactupicrinal 1H NMR

I'm having trouble understanding which hydrogens are magnetically distinct in the following molecule (lactupicrinal): I've counted all the hydrogens (there are 20) and I know that hydrogens in a ...
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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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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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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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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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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 ...
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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 ...
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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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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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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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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: ...
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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 ...
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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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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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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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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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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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337 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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