Even small molecules can yield very complex 1H NMR spectra as the result of spin - spin coupling. This is particularly true for small molecules that contain fluorine. It can sometimes be challenging to determine which splittings are due to 1H-1H coupling and which are due to 1H-19F coupling. One can collect a 1H spectrum with 19F decoupling to give a spectrum with only 1H-1H coupling present. Even with this data, it may be difficult to evaluate the 1H-19F coupling constants by comparing the 1H[19F] spectrum to the 1H spectrum due to the complexity of the multiplets. The 1H-19F coupling constants can however be read directly from a 1H PSYCHE spectrum. The PSYCHE spectrum provides a 1H decoupled 1H spectrum, leaving only the 1H-19F coupling behind. The bottom trace of the figure below shows the 300 MHz 1H NMR spectrum of 2,3-difluoro pyridine. The spectrum is quite complex, making it difficult to assign 1H-1H and 1H-19F couplings. The middle trace shows the 1H[19F] spectrum which allows the evaluation of all of the 1H-1H coupling constants (3JH5-H4 = 4.8 Hz, 4JH5-H3 = 1.6 Hz and 3JH4-H3 = 8.0 Hz. The top trace shows the 1H PSYCHE spectrum which allows one to evaluate all of the 1H-19F coupling constants. For this compound, 4JH3-F1 = 3JH3-F2 = 9.8 Hz, 4JH4-F2 = 3.2 Hz and 4JH5-F1 = 1.8 Hz.
[Question from NMRWiki Q&A forum] C-C coupling constants measurement
C-C coupling constants measurement
Hello,I'm trying to set up an experiment to measure C-C coupling constants:1. Do I understand it right that the standard 1D INADEQUATE pulse sequence inad1d would give me quite and accurate measurement of 1J(C-C) constants and the resulting spectrum can be treated similarly to a regular 1H spectrum, i.e. if the carbon in question is a secondary one, its signal will come out as a doublet of doublets?
2. What's the easiest method to measure long-range C-C coupling constant? I have read about SELINQUATE, J-modulated ADEQUATE, GRECCO and modified refocused...
nmrlearner
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08-26-2015 11:52 PM
[U. of Ottawa NMR Facility Blog] Measurement of Long Range C H Coupling Constants
Measurement of Long Range C H Coupling Constants
The stereochemistry of compounds is assigned very often with proton - proton NOE's by applying the 2D NOESY technique or the 1D selective gradient NOESY technique. These methods fail, however when the distance between protons is too large to measure an NOE. When faced with this situation, it may be possible to measure long range proton - carbon coupling constants which are able to provide the necessary information. Three-bond carbon - proton couplings follow a Karplus relationship where the magnitude of the coupling constant is related to...
nmrlearner
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08-17-2012 10:44 PM
On the calculation of 3Jαβ-coupling constants for side chains in proteins
On the calculation of 3Jαβ-coupling constants for side chains in proteins
Abstract Structural knowledge about proteins is mainly derived from values of observables, measurable in NMR spectroscopic or X-ray diffraction experiments, i.e. absorbed or scattered intensities, through theoretically derived relationships between structural quantities such as atom positions or torsional angles on the one hand and observable quantities such as squared structure factor amplitudes, NOE intensities or 3 J-coupling constants on the other. The standardly used relation connecting 3 J-couplings...
nmrlearner
Journal club
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06-25-2012 04:41 AM
Conformational dependence of 13C shielding and coupling constants for methionine
Abstract Methionine residues fulfill a broad range of roles in protein function related to conformational plasticity, ligand binding, and sensing/mediating the effects of oxidative stress. A high degree of internal mobility, intrinsic detection sensitivity of the methyl group, and low copy number have made methionine labeling a popular approach for NMR investigation of selectively labeled protein macromolecules. However, selective labeling approaches are subject to more limited information content. In order to optimize the information available from such studies, we have performed DFT...
nmrlearner
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08-25-2010 03:51 PM
[NMR paper] The impact of direct refinement against three-bond HN-C alpha H coupling constants on
The impact of direct refinement against three-bond HN-C alpha H coupling constants on protein structure determination by NMR.
Related Articles The impact of direct refinement against three-bond HN-C alpha H coupling constants on protein structure determination by NMR.
J Magn Reson B. 1994 May;104(1):99-103
Authors: Garrett DS, Kuszewski J, Hancock TJ, Lodi PJ, Vuister GW, Gronenborn AM, Clore GM
nmrlearner
Journal club
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08-22-2010 03:33 AM
[NMR paper] The impact of direct refinement against three-bond HN-C alpha H coupling constants on
The impact of direct refinement against three-bond HN-C alpha H coupling constants on protein structure determination by NMR.
Related Articles The impact of direct refinement against three-bond HN-C alpha H coupling constants on protein structure determination by NMR.
J Magn Reson B. 1994 May;104(1):99-103
Authors: Garrett DS, Kuszewski J, Hancock TJ, Lodi PJ, Vuister GW, Gronenborn AM, Clore GM
nmrlearner
Journal club
0
08-22-2010 03:33 AM
[U. of Ottawa NMR Facility Blog] E.COSY and the Relative Signs of Coupling Constants
E.COSY and the Relative Signs of Coupling Constants
Spin-spin coupling constants can have values greater than or less than zero. The absolute sign of the coupling constants cannot be discerned from the simple examination of a 1H NMR spectrum. The E.COSY1 (Exclusive COrrelation SpectroscopY) technique is one method which can be used to determine the relative signs of coupling constants. E.COSY is a phase sensitive COSY variant which produces off-diagonal signals showing only the active coupling (i.e. the coupling directly responsible for the cross-peak) as 2x2 antiphase square tetrads...
PSYCHE to Evaluate 1H-19F Coupling Constants
Linear Mode
