9
votes
Accepted
What's the exact mechanism of spin coupling in NMR?
In a system with only one spin, the energy levels available to that spin depend on the strength of the external magnetic field (there is a direct proportionality).
In more complex systems, spin–spin ...
- 71.1k
8
votes
Predicted H NMR spectrum shows two signals for NH2 group
The amino group can be conformationally locked by an intramolecular hydrogen bond:
by formation of a five-membred cycle. (And in organic chemistry, the formation of five, and to some lesser degree ...
- 28.4k
7
votes
Accepted
NMR and dienes to isolate certain isotopes?
There are at least two glaring problems:
Look at the energy scales on which NMR operates (for example, take the resonance frequency $\nu$ and calculate the associated energy $h\nu$)... and compare it ...
- 71.1k
7
votes
Interpreting NMR: what does it mean when there are two signals when there should be (and looks like) only one, and integration where there is no peak?
It's impossible to see from your spectrum whether there's one or two peaks. You need to zoom in.
But I get the sense you're referring to the 'peaks' at the top (i.e. the numbers) which are chosen by ...
- 71.1k
5
votes
Why are fluorine-19 NMR spectra less affected by paramagnetic centers than other common nuclei?
$\ce{^{19}F}$ has similar NMR properties to $\ce{^1H}$ except in particular for the much larger chemical shift tensor terms and resulting larger chemical shift anisotropy (CSA). As a result CSA ...
- 20.9k
5
votes
Accepted
1H-NMR: How does the oxygen in ethers act as a spin coupling barrier while the oxygen in hydroxy groups doesn't?
Hans Reich's website remains a treasure trove of NMR information that you can consult for theory and values of J couplings. All of the following comes from that site.
First, on the origin of through-...
- 20.9k
5
votes
NH protons not appearing in H NMR spectrum of 3,4-dihydropyrimidone derivative (solvent: CDCl3)
As indicated by @Waylander, your compound may undergo keto-enol tautomerism. Beside a sample which may contain varying concentrations of three compounds (top row), ...
- 28.4k
4
votes
NMR and dienes to isolate certain isotopes?
Look up the difference of the isotopic masses between hydrogen and deuterium (a factor of about 2),* and the two isotopes of uranium (difference here $\approx1.5\%$), e.g. in NIST's table of atomic ...
- 28.4k
4
votes
How to interpret this pair of IR and 1H NMR spectra?
I was spoiled working with a FTIR with digital spectra and libraries. I no longer have access so I can give some bits and pieces. First there is no OH! the blip at 3400 and strong peak at 1730 ...
- 1,820
2
votes
NMR Spectra Oddities
There is a very simple anwer: these methylene groups are practically chemically equivalent. It is impossible to make a specific reaction with one of them.
Chemically equivalent hydrogens have the same ...
- 12k
2
votes
Why are different Aluminium valencies observed from NMR and what logic can be used to normalise molar ratios of different valency atoms?
Are you sure that the different 27Al resonances you observed are due to varying oxidation numbers? While I don't have a complete understanding of the materials you are using, I do have experience with ...
- 101
1
vote
H-NMR Analysis of C15H24O
This is a good fit for 2,6-di-tert-butyl-4-methylphenol. See the 1H spectrum here
- 21.6k
1
vote
evaporating DMSO/Ethanol
The boiling point of DMSO is about 462 kelvin and that of ethanol is about 352 kelvin, you should be able to evaporate ethanol with ease without losing any of the DMSO solvent. For fast evaporation, ...
- 2,162
1
vote
Correlation between 1H and 13C shifts - coincidence or not?
It is true that a quick glance at any given table of typical chemical shifts will reveal that the chemical shifts of protons $(\delta_\ce H)$ tend to correlate pretty well with the chemical shifts of ...
- 39.5k
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