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
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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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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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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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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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1answer
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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 ...
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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
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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 ...
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1answer
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Organic Chemistry Help Please! [closed]

I'm not sure how to even start these two problems. How do you predict the structure of something when its molecular formula isn't provided to you? Also how do you calculate percent purity from this ...
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NMR - coupling of chemically equivalent protons

In Klein's Organic Chemistry 3rd Edition page 671, it states This observation, called the n + 1 rule, only applies when all of the neighboring protons are chemically equivalent to each other. ...
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1answer
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Why do carboxylic acid derivatives show a more upfield shift than carbonyls in 13C-NMR?

The prototypical 13C NMR shifts of carbonyl carbons is in the range 190–200 ppm, however, carboxylic acid derivatives have a 13C NMR shift in the range 160–180 ppm instead. What structural factors ...
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1answer
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What is number of 1H NMR signals for toluene?

I am searching the web for the number of 1H NMR signals of toluene and I find two different results. Some say there are two signals while others say there are four (According to me, it should be 4). ...
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Is there a real detection limit in NMR spectroscopy?

From what I've read, my impression is that with a sufficient number of scans etc., one can get spectra from even very dilute samples (S:N ratio ~ $\sqrt{\text{NS}}$). Obviously, this is not always ...
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How does the presence of various NMR active nuclei in a compound affect coupling and signal multiplicity?

I am basically wondering how the presence of various NMR active nuclei present in a organic molecules affect the shift values and coupling states normally seen in a molecule lacking these nuclei. ...
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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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What is the identity of the unknown compound using GCMS and NMR?

I've been asked to identify an unknown compound by performing several analytical techniques on it. The compound was a white powder and had a boiling point of 65 degrees celsius. I have the GC mass ...
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Are aliphatic amines SABRE amenable?

Hyperpolarization of molecules via the SABRE-SHEATH technique is a fairly new idea. Does anybody know if hyperpolarizing aliphatic nitrogens is possible? The articles I've read mostly use N-...
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Utility of proton vs carbon NMR

I've just learnt about both types of NMR, and I haven't ever used NMR in real life, so anything I say may be wrong. The crux of this question is that, in my own opinion, proton NMR gives you more ...
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Magnetic non-equivalence of acetal protons

I have been using bromoacetaldehyde diethyl acetal recently and noticed something interesting about the 1H NMR. The methylene protons of the ethyl acetal are magnetically non equivalent. You see two ...
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1answer
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Paramagnetic relaxation in 13C nmr

I'm trying to make my 13C{1H} (hydrogen decoupled) nmr more quantitative. From the literature I've noticed that researchers either increase the delay time in the experiment (which I can't do, as it ...
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Comparison of chemical shifts among alkanes in NMR spectroscopy

I was reading through the factors influencing chemical shifts in proton NMR. I found the order of chemical shifts in the image above. Why is this order supposed to be as it is? I thought it would be ...
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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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1answer
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NMR spectrum of 3-hexylthiophene: why is the methyl group not a triplet?

I have an example spectrum, and it shows which peaks correspond to which H, but I don't understand why the spectrum looks like that e.g. I would expect the peak at 0.88 to be a triplet based on the (...
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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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1answer
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Assignment of the 13C NMR of 2-heptanone

The 13C NMR of 2-heptanone is given below: I understand the assignments of the carbons labelled 7, 6, 4 and 1. My question is: Why is the shift of environment 5 higher than that of 3, despite being ...
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1answer
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H1 NMR Spectra of inorganic complex, Cu4OCl6(2-mepy)4

I'm having difficult interpreting the following H1 NMR I have been given for Cu4OCl6(2-mepy)4. The NMR spectra obtained with integration trace beneath. I'm not too sure how to rationalise the 4.5:1 ...
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NMR Spectra Oddities

I've noticed that as the chain length of n-alkanes increase, their number of carbon environments tend to 5 peaks, and no more, no less. Why is this? I've looked on multiple NMR (C13 NMR, I might add) ...
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Matching the NMR to a compound

I was given a molecule that I had to identify the NMR of. The molecule is 2-methylpent-1-ene (shown below): The correct NMR spectra for this molecule is: My question is, why is this the right ...
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1answer
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Why is it necessary to measure the NMR frequency relative to a standard such as TMS?

The horizontal axis of an NMR spectrum is "chemical shift". A standard environment such as tetramethylsilane is chosen as the zero of chemical shift. The frequency at which resonance occurs for other ...
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Directionality of ring current-induced magnetic fields in purines

What would be the directions of ring current-induced magnetic fields in purine-like heterocycles in a ​strong magnetic field? Would be the antiparallel state be a default state for these substances in ...
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1answer
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Percentage of trans-stilbene traces in cis-stilbene H NMR

This is H NMR spectrum of cis-stilbene. There are some traces of trans stilbene. I have to determine how many trans-stilbene is present, the exact percentage and I have problem with that. I guess ...
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Zero filling leading to increases in resolution (NMR)

Zero-filling involves adding data points with zero intensity to the end of an FID. According to this website https://www2.chemistry.msu.edu/facilities/nmr/handouts/DH%20NMR%20Basics.pdf zero filling ...
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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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Assigning the 13C NMR spectrum of bromobenzene and 4-bromobenzophenone

I've been trying to assign the peaks of 4-bromobenzophenone (I have the peaks, just need to assign them to the correct carbons), but my assignments and what it should be don't seem to agree. As part ...
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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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Do most methylene groups sandwiched between a carbonyl and aryl group have a chemical shift around 3.5 ppm?

For example, take methyl phenyl acetate, we can see the chemical shifts is at 7.4 ppm, singlet, 5H; 3.6 ppm, singlet, 3H and 3.5 ppm, singlet 2H. Let us say we didn't know the identity of the compound ...
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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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Prop-2-yn-1-ol NMR spectrum differences

Looking at prop-2-yn-1-ol spectrum that was taken from: Spectrometric identification of organic compounds. Robert M. Silverstein and G. Clayton Bassler. J. Chem. Educ., 1962, 39 (11), p 546. DOI: 10....
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Where does magnetic inequivalence come from?

As the question says, I'm having trouble understanding where does magnetic inequivalence in $\ce{^1H}$ NMR come from. All the sources I've found say that two protons are magnetically equivalent ...
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Why does Carbon-13 NMR not have splitting patterns?

I read about splitting patterns in proton NMR and found that this is due to spin-spin coupling, where reference to Pascal's triangle can explain the splitting patterns found in doublet, triplet and ...
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1answer
297 views

Unsaturated ketone coupling pattern

Can someone explain to me the coupling pattern by proton $5$? Why is it triplet of quintet? Is it long range coupling? I'm assuming that the proton $5$ couples to two other protons on carbon $4$. ...
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1answer
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(S)-glycidyl benzyl ether NMR problem

Can someone explain the appearance of the resonances at $\pu{4.6 ppm}$ (spectrum taken from here)? Is it due to long range coupling? But the coupling constants are too high for such long range ...
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CH2 group in alkyl glucoside gives two separate HNMR signals

Zoom in: It seems like the CH2 next to the sugar gives two different NMR signals which is very interesting. Could someone explain me why?
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Nitrobenzene and other monosubstituted benzenes 1H vs 13C NMR assignments

The reported 1H NMR spectrum for nitrobenzene has three signals corresponding to H2/H6, H3/H5 and H4, respectively. The signals (ppm) appear at 8.25 (H2/H6), 7.71 (H4), and 7.56 (H3/H5). This is, the ...
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How can multiplets in para-disubstituted benzene rings be described?

How should I label the multiplicity of the aromatic signals in an 1H-NMR spectrum with the following substitution pattern? I have seen lots of people labeling both signals in this kind of system as ...
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1answer
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Slight variation in NMR integrals of CH protons vs. CH2 or CH3

While acquiring some NMRs I find that there is a consistent pattern in that protons attached to sp2 carbons tend to have slightly smaller integrals than protons attached to sp3 carbons: (peaks in ...
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H-NMR spectroscopy of [18]annulene

Why does [18]annulene show only one peak in its proton NMR at $\pu{100^\circ C}$? Does any structural change happen such that all the hydrogens are alike?
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Deduce the possible structure given spectroscopic data for the aromatic compound

For $\ce{C11H13NO}$, I have the following $\ce{^1H}$ NMR data: shift (ppm) 3.00 (6H, s) 6.55 (1H, dd, $J=15.5, \pu{9 Hz}$) 6.70 (2H, d, $J=\pu{8Hz}$) 7.35 (1H, d, $J=\pu{15.5Hz}$) 7.45 (2H, d, $J=\...
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1answer
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How can I figure out which coupling constants match which hydrogen?

I am looking for some guidance assigning the $J$ coupling constants to the corresponding hydrogens. Here is my data: I can obviously see that shift 3.56 is for the methyl group. I can also see that ...
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1answer
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How can Hydrogen NMR be used to distinguish between these two isomers?

I am having trouble explaining how and why the spectra of these two compounds would differ: I am sure it has something to do with how the protons will couple. In the first isomer (left), the protons ...
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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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