Automatic first-order multiplet analysis in liquid-state NMR

Organic Letters, 2004

An approach relying on quantum mechanical calculations of proton−proton and proton−carbon J coupling values is proposed as a tool for assigning the relative configuration on chiral organic compounds. The method is suitable for carbon frameworks containing several adjacent stereogenic centers and may allow significant advances in the extensive use of spin−spin couplings in structural elucidation.

Theoretical Chemistry Accounts, 2007

Work on computational NMR recently carried out at our Laboratory in Padova is reviewed. We summarize our results concerning the calculation of NMR properties (chemical shifts and spin–spin coupling constants) in a variety of contexts, from the structure elucidation of complex organic molecules or molecules containing heavy atoms to weakly interacting species, such as those involved in hydrogen bonding or van der Waals CH-π interactions. We also present some original results, viz. the calculated 1H and 13C spectra of the putative natural substance nimbosodione, the first examples of calculated 181Ta chemical shifts, spin–spin couplings in $\hbox{Hg}_{4}^{2+}$ and through-space coupling constants involving 205Tl.

Chemical Physics Letters, 2013

Zero-field nuclear magnetic resonance (NMR) spectroscopy is emerging as a new, potentially portable, and cost-effective NMR modality with the ability to provide information-rich, high-resolution spectra. We present simple rules for analysis of zero-field NMR spectra based on first-order perturbation theory and the addition of angular momenta. These rules allow for the prediction of observed spectral lines without numerical simulation. Results are presented for a few small organic molecules with characteristic spin topologies, demonstrating unambiguous assignment of peaks, highlighting the potential of zero-field NMR as a tool for chemical identification.

Arkivoc, 2004

Pattern recognition is extremely important for both structure elucidation and stereochemical studies as a means for the measurement of spin-spin coupling constants. Many treatises deal with the formation of splitting trees to create a pattern for a given set of spin-spin coupling constants. We present here a general systematic procedure to easily analyze first order multiplets in NMR spectroscopy. This method has the advantage of measuring coupling constants while deconvolving the signals at the same time using an extension of the modified J doubling in the frequency domain.

The Journal of Physical Chemistry A, 2009

Multidimensional nuclear magnetic resonance (NMR) experiments measure spin-spin correlations, which provide important information about bond connectivities and molecular structure. However, direct observation of certain kinds of correlations can be very time-consuming due to limitations in sensitivity and resolution. Covariance NMR derives correlations between spins via the calculation of a (symmetric) covariance matrix, from which a matrix-square root produces a spectrum with enhanced resolution. Recently, the covariance concept has been adopted to the reconstruction of nonsymmetric spectra from pairs of 2D spectra that have a frequency dimension in common. Since the unsymmetric covariance NMR procedure lacks the matrix-square root step, it does not suppress relay effects and thereby may generate false positive signals due to chemical shift degeneracy. A generalized covariance formalism is presented here that embeds unsymmetric covariance processing within the context of the regular covariance transform. It permits the construction of unsymmetric covariance NMR spectra subjected to arbitrary matrix functions, such as the square root, with improved spectral properties. This formalism extends the domain of covariance NMR to include the reconstruction of non-symmetric NMR spectra at resolutions or sensitivities that are superior to the ones achievable by direct measurements.

Magnetochemistry

In this work, 242 NMR spin–spin coupling constants (SSCC) in 20 molecules are calculated, either with correlated wave function methods, SOPPA and HRPA(D), or with density functional theory based on the B3LYP, BHandH, or PBE0 functionals. The calculations were carried out with and without treatment of solvation via a polarizable continuum model in both the geometry optimization step and/or the SSCC calculation, and thereby, four series of calculations were considered (the full-vacuum calculation, the full-solvent calculation, and the two cross combinations). The results were compared with experimental results measured in a solvent. With the goal of reproducing experimental values, we find that the performance of the PBE0 and BHandH SSCCs improves upon including solvation effects. On the other hand, the quality of the B3LYP SSCCs worsens with the inclusion of solvation. Solvation had almost no effect on the performance of the SOPPA and HRPA(D) calculations. We find that the PBE0-based...

Journal de Chimie Physique et de Physico-Chimie Biologique, 1998

La mesure des constantes de couplage est un probl6me gCnCral en Resonance MagnCtique NuclCaire des liquides pour lequel de nombreuses solutions ont CtC propodes. La mCthode exposCe ici fait intervenir une transformation des donnCes dans le domaine des temps qui fournit un graphe de la multiplicitC en fonction de la valeur de J. L'efficacitC de la mCthode est dCmontrCe sur le spectre de RMN 1H du mbromonitrobenzkne, qui prksente des couplages de faible valeur difficiles 2 merxirer directement. mots-clCs : RMN, constantes de couplage, analyse automatique.

Magnetic Resonance in Chemistry, 2005

New NMR pulse schemes completely driven under homonuclear and heteronuclear cross-polarization conditions are proposed for the study and the measurement of coupling constants in symmetrical molecules in solution. The appropriate superimposition of independent magnetization components can afford several spin-selective multiplet patterns that are suitable for the determination of the magnitude and the sign of proton-proton and proton-carbon coupling constants with optimum sensitivity levels. A detailed product operator formalism analysis for the proposed doubly selective 1D and nonselective 2D HCP-TOCSY versions is provided and experimental verification for the configurational analysis of symmetric olefinic systems having chemical equivalence is demonstrated.

Analytical chemistry, 2017

The exceptionally rich information content of nuclear magnetic resonance (NMR) spectra is routinely used to identify and characterize molecules and molecular interactions in a wide range of applications, including clinical biomarker discovery, drug discovery, environmental chemistry, and metabolomics. The set of peak positions and intensities from a reference NMR spectrum generally serves as the identifying signature for a compound. Reference spectra normally are collected under specific conditions of pH, temperature, and magnetic field strength, because changes in conditions can distort the identifying signatures of compounds. A spin system matrix that parameterizes chemical shifts and coupling constants among spins, provides a much richer feature set for a compound than a spectral signature based on peak positions and intensities. Spin system matrices expand the applicability of NMR spectral libraries beyond the specific conditions under which data were collected. In addition to b...

Journal of Magnetic Resonance, 1998

An existing algorithm, founded on the works of Stephenson and There is a basic difference between the traditional CB-B Binsch, for the automatic analysis of isotropic or simple anisoapproach and automatic analysis programs since, in the fortropic NMR spectra has been improved to treat very complex mer, many hours of an experienced operator's time are re-NMR spectra of molecules dissolved in nematic solvents. The main quired, whereas what is needed in the latter is (ideally) just options added to the original algorithm are a wider choice of CPU time. smoothing functions; the use of the principal component regression There is not yet an automatic procedure for anisotropic method; and the possibility of selecting molecular coordinates, spectra with performance comparable to that for isotropic order parameters, and spectral parameters as variables of the probspectra. The difference in behavior can be easily understood lem. By means of these new options, it has been possible to analyze by recalling that anisotropic spectra differ from isotropic automatically NMR spectra (even depending on 27 spectral parameters) of 16 molecules in an anisotropic environment. Details spectra in that they lack the typical cluster structure of the of each case are discussed. ᭧ 1998 Academic Press latter. As far as we know, the only programs of this kind are DANSOM (7) and DAISY (8), both implementations of DAVINS, where the spin Hamiltonian has been modified in order to deal with dipolar couplings (as a further improve-1