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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26
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4answers
6k views

Why don't equivalent hydrogens cause splitting in NMR?

When doing NMR spectroscopy, it is an observed fact that equivalent hydrogens do not split one another. Why don't equivalent hydrogens split each other's signals? For example, why is the NMR spectrum ...
23
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3answers
772 views

What is the isomer distribution in monosubstituted fluorobullvalene?

Bullvalene (tricyclo[3.3.2.02,8]deca-3,6,9-triene) is a fluxional molecule able to interconvert any two carbon atoms through a series of degenerate Cope rearrangements (for more information, see the ...
13
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2answers
1k views

NMR chemical shift range of different elements

A typical $\ce{^1H}$ NMR runs from approximately 0 to 10 ppm, give or take a bit. $\ce{^13C}$ NMR runs from 0 to 200. And $\ce{^59Co}$ NMR runs from -5000 to 15000 ppm! There seems to be some ...
10
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1answer
871 views

Symmetry and NMR linewidths of quadrupolar nuclei

The linewidth of peaks when taking NMR spectra of quadrupolar nuclei (11B or 14N for example) is often very broad, making their interpretation challenging. Recently, when acquiring 11B-NMR spectra ...
9
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3answers
949 views

Difference between S and I in the context of magnetic resonance experiments

In the lecture our professor told us that nuclei with $S>1/2$ have a quadrupole and are therefore detected with NQR instead of NMR. The majority of all elements have nuclei with $S>1/2$. I ...
4
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2answers
394 views

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?
19
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3answers
3k views

Modern open-source tools for simulation of NMR spectra

I am interested in predicting the NMR spectrum of small organic compounds. It doesn't matter to me if the prediction is very accurate. I'll eventually be comparing the prediction to experimental ...
7
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3answers
1k views

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 ...
5
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1answer
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What is the proton NMR spectrum of p-methoxyphenol?

I think there will be two pairs of doublets, since the hydrogens adjacent to the $\ce{OCH3}$ and those adjacent to the $\ce{OH}$ group will be in different environments. The answer, however, is that ...
13
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4answers
22k views

Why do hydroxyl groups only produce a singlet in proton NMR?

Take, for example, methanol ($\ce{CH3OH}$). The hydroxyl proton ($\ce{-O$\color{red}{\ce{H}}$}$) is three bonds away from three more protons ($\ce{-C$\color{blue}{\ce{H}}$_3}$), which aren't ...
3
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1answer
846 views

Spin spin coupling in a proton NMR of an ester?

I am learning about proton NMR and spin-spin coupling, and am confused about whether splitting occurs over an ester bond. Specifically, in the case of ethyl methanoate, HCOOCH2CH3, if I were to number ...
3
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1answer
419 views

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 ...
2
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1answer
2k views

Suggest possible structures for the compound PF3(Ph)(NMe2) using the NMR data

use these data to suggest the possible structure for the compound PF3(Ph)(NMe2): 19F Spectrum, two signals: a doublet of doublets, J=56 and 819Hz, -39.5ppm, relative intensity 2 a doublet of ...
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1answer
146 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, but ...
12
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1answer
5k views

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 ...
16
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2answers
297 views

Correlation between 1H and 13C shifts - coincidence or not?

A quick glance at any table of typical chemical shifts will reveal that the chemical shifts of protons $(\delta_\mathrm H)$ tend to correlate pretty well with the chemical shifts of the carbons to ...
35
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3answers
22k views

Splitting of multiplets in ¹H NMR spectra?

I'm currently taking VCE (Victorian Certificate of Education) Chemistry classes, and we're currently studying the interpretation of spectra produced by Hydrogen NMR (Nuclear Magnetic Resonance) ...
9
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3answers
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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 signal ...
9
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3answers
822 views

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 ...
8
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2answers
3k views

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?
7
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2answers
253 views

Open resource for spectroscopic raw data

Is anyone aware of reliable resources (ideally public) which allow the user to download the raw spectroscopic data such as infrared spectrum of small organic molecules, or rotational spectrum of HCl/...
6
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2answers
23k views

Why don't labile protons such as -OH and -NH have a characteristic chemical shift?

Is it simply because the H instantly disassociates so it is a proton with zero shielding?
15
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1answer
1k views

What is deuterium-depleted water actually used for?

I noted, flipping through the paperback Alfa Aesar catalogue today, that they sell deuterium-depleted water. Under the usage category, they list 'NMR'. I'm trying to work out what specific use this ...
12
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1answer
541 views

19F NMR of hexafluorobromine(VII) cation

$\ce{[BrF6]+}$ is an octahedral species, and should have only one fluorine environment due to the symmetry. $\ce{Br}$ has nuclear spin $I=3/2$ and therefore is unlikely to cause splitting due to rapid ...
9
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1answer
9k views

What is the origin of 'tenting' or 'roofing' in NMR spectra?

Given an NMR spectrum with two coupled nuclei one can often observe so-called 'roofing' – an asymmetry in the multiplet. For example, here is a 300 MHz proton spectrum of 1-bromo-2-methoxyethane, ...
6
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1answer
2k views

Why is a squared cosine window function commonly used for 2D spectra?

In nearly all default parameter sets for 2D NMR experiments on Bruker spectrometers, the window function is set to a pure squared cosine function for both dimensions (...
5
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2answers
181 views

Sensitivity of Carbon NMR Compared to Proton NMR

I am trying to figure out exactly how much less sensitive carbon NMR is from proton NMR. In a lecture, my professor said that carbon NMR is 1/5800th as sensitive as proton NMR for the following ...
4
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1answer
3k views

Most negative and most positive value for proton chemical shifts

What are the most negative and the most positive values for proton chemical shifts recorded till present?
4
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3answers
3k views

How to identify an unknown compound with spectroscopic data?

I need some help identifying the following unknown compound. Any suggestions or hints regarding the possible compound would be highly appreciated. So far I am thinking the broad peak on the IR is an ...
3
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1answer
2k views

NMR: Magnetic and chemical equivalence in benzene

According to my textbook, all the protons in $\ce{^{12}C_6{}^{1}H_6}$ are magnetically equivalent, but those in $\ce{^{13}C_6{}^{1}H_6}$ are not. I understand that for two nuclei to be magnetically ...
3
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1answer
14k 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 ...
3
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2answers
103 views

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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2answers
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Comparison of COSY and TOCSY for detection of small couplings between protons

I routinely run COSY spectra to help with assignment of my proton NMR. The experiment is fast to run and generally useful, however some of the intermediates I've recently been making have had ...
11
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2answers
5k views

Why are all the phenyl protons in benzyl alcohol equivalent in the ¹H-NMR spectrum?

Below is a $\ce{^1H}$ Nuclear Magnetic Resonance (NMR) spectrum for benzyl alcohol. The hydrogen in the alcohol group gives rise to a unique signal. The two hydrogens in $\ce{CH2}$ give rise to a ...
7
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1answer
5k views

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 ...
6
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2answers
30k views

How to assign the signals in the H-NMR of Aspirin?

I need to assign the H-NMR of aspirin, below is aspirin with the H's labelled. The peaks I have are: 2.30ppm (I this is a singlet and would be F) 7.07ppm (I think this is E) 7.29ppm (...
5
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1answer
1k views

Why is the Gaussian Window Function used to enhance resolution in 1D NMR spectra?

In a recent question it was explained that Gaussian window functions are not used in 2D NMR spectra as they can introduce artifacts into the spectrum baseline by truncating the FID. Why then are they ...
5
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2answers
2k views

How do I find out what benzene containing compound this is with IR and NMR?

I have the following IR and NMR of an unknown substance. Can someone tell me what is a possible structure of the compound or point me in the correct direction. So far I am thinking of a benzene ring ...
5
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1answer
4k views

Why is the para carbon in Benzaldehyde NMR more deshielded than the ortho and meta carbons?

Assuming this image is correct, why is the Carbon-3 more deshielded than Carbon-2 and Carbon-1? From what I understand, deshielding is the greatest when the Carbon atom is closer to electron ...
3
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2answers
2k views

How many total absorptions would appear on proton -NMR spectrum for this molecule?

I count 7 equivalent absorptions total, but answer says 8. I don't see where this eighth absorption comes from? Heres how I'm counting starting on right side of molecule: 1 is Carbox acid H 2 is ...
3
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1answer
1k views

1H NMR splitting of 3-methyl-1-butanol

I have a question about 1H NMR splitting of 3-methyl-1-butanol. The spectrum looks as the following. The assignment of the NMR spectrum is the following. ...
3
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1answer
475 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 ...
3
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1answer
7k views

NMR spectrum of cyclohexanol - hints on integration

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 ...
3
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1answer
1k views

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 ...
2
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1answer
793 views

13C NMR of bromobenzene ipso carbon shielding

I've got a $\ce{^{13}C}$ NMR spectrum for bromobenzene. The ipso carbon is significantly more shielded (appearing upfield) than the two ortho carbons. Why is this? Wouldn't the electron-withdrawing ...
2
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1answer
1k views

1H NMR of p-methoxy phenol, 32 possible lines?

This is a follow-up question, emerging from answering this one. The Silverstein book 1 aims to rise awareness that not every 1H NMR signal that on first inspection may look like a doublet actually is ...
2
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1answer
298 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?
2
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1answer
2k views

Chemical shift value and proton NMR spectroscopy

I am a bit confused about what chemical shift value signifies in proton NMR spectroscopy. If the proton of the standard substance TMS absorbs X Joules of energy to go into resonance, than a substance ...
2
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2answers
880 views

Ring currents of anti-aromatic and aromatic systems

Why are ring currents associated with aromatic systems diamagnetic while those of anti-aromatic systems are paramagnetic? Does it have anything to do with the number of delocalised electrons 4n+2 and ...
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2answers
78 views

Diastereotopic methylene protons in achiral molecules

Are the protons in methylene groups of achiral molecules such as propane-1,2,3-triol or 3-hydroxypentanedioic acid diastereotopic? Consider propane-1,2,3-triol. To me, replacing one of the protons in ...