Did you know that you can observe ¹H-¹⁴N coupling not only in highly symmetrical ammonium salts, but also in isonitriles?
In most compounds containing nitrogen, even including some in which hydrogen is bonded directly to nitrogen, the electric field gradient about the ¹⁴N nucleus is sufficiently strong to decouple either partially or completely the ¹⁴N and ¹H spins through quadrupole relaxation. The fact that splitting is observed with isonitriles indicates that the electric field gradient is unusually small and that the spin-lattice relaxation time of ¹⁴N must be comparable to the coupling constant. The low electric field gradient must be due to the axial symmetry of the electron density near the nitrogen atom. DETAILS: dx.doi.org/10.1063/1.1732106

Here, you can also see a great example of using the HOMOdecoupling technique: we selectively irradiate the signal at ~2.0 ppm to remove its coupling with the signal of interest at 3.37 ppm.
#spin #coupling #nitrogen

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It’s #NMRWeekend‼️ The purpose of this post is not only to present a quiz but also to demonstrate the importance of fluorine decoupling (the spectrum on the right) during the ¹H acquisition of fluorinated aromatics. Use the poll below ?.
#fluorine #spin #coupling
NOTE: Fluorine spectrum is proton decoupled!

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Why are paramagnetic samples a challenge for NMR? ?*?
In the presence of paramagnetic impurities, the lifetime of the exited spin states is shortened due to interactions with the fluctuating magnet fields that arise from unpaired electrons. This significantly impact your NMR experiment:*
?Shorter T₁ and T₂ relaxation times: signal broadening and peaks vanishing.
? Distorted Chemical Shifts: Paramagnetic interactions can shift signals far from their expected positions, complicating analysis.
Because the magnetic moment of an unpaired electron is larger than the nuclear magnetic moment by a factor of about 1000, this mechanism is very effective and paramagnetic compounds can normally not be measured by NMR. Even the presence of trace amounts of oxygen, a paramagnetic molecule, shows the line broadening effect and for a precision of better than 0.1 Hz the sample tubes have to be
degassed on the vacuum line and sealed.
Some common types of paramagnetic contaminants include: Transition Metals: Examples include iron (Fe²⁺/Fe³⁺), manganese (Mn²⁺), cobalt (Co²⁺/Co³⁺), nickel (Ni²⁺), and copper (Cu²⁺). Lanthanides: Such as gadolinium (Gd³⁺), dysprosium (Dy³⁺), and europium (Eu³⁺), often used in NMR as relaxation agents or shift reagents but problematic as contaminants. Free radicals, such as those generated in chemical reactions (e.g., organic radical species), can act as paramagnetic contaminants.

?In this ¹H spectrum, you can clearly see how the peaks are broadened and distorted, rendering the data nearly unusable!

? NMR of paramagnetic compound has a lot of practical aspects though. See the following links for example:
Link 1
Link 2
(or Google “NMR of paramagnetic compounds”)

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Is there a way to calculate the spin coupling constant between equivalent nuclei❓ Yes, there is ❗️For this purpose, you need the corresponding deuterated isotopomer and a well-recorded ¹H NMR spectrum☝️ Details are in the picture.
#spin #coupling

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It’s #NMRweekend ⁉️? Use the poll below ?. This is an experimental spectrum. The explanation for the challenge will be published in a few days ?.
#nmrchallenge #quiz

✅ UPD: The correct answer is A.
1. The aromatic protons’ spin coupling constant of 8.3 Hz eliminates B.
2. The spin coupling patterns of the aliphatic CH₂ groups show that they are all in the same spin system, which eliminates C.

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