Correlation NMR techniques

Andersen, 0.M., Aksnes, D.W., Nerdal,W., and Johansen, O.P. 1991a. Structure elucidation of cy-anidin-3-sambubioside and assignments of the H and 13C NMR resonances through two-dimensional shift-correlated NMR techniques. Phytochem. Anal. 2 175-183. 

A Ci-symmetric cis-1 bis-adduct with an additional bridge between the addends was obtained in the reaction between two molecules of ethyl propio-late and C6o in the presence of triphenylphosphane.318 Its structure (( )-162, Figure 1.37) was established with the help of the HMBC- (heteronuclear multiple bond correlation) NMR technique and includes stereogenic centers in the addend moiety as well as a noninherently chiral addition pattern. The latter can be related to the head-to-tail connectivity of the two propiolate units. 

The present chapter deals with the application of advanced, proton detected, heteronuclear H- Sn correlation NMR techniques [16-20] to the structure elucidation of organotin compounds, especially of the coordination sphere of their tin atoms and their hypervalency characteristics. 

Application of two-dimensional shift correlated NMR techniques to the structure determination of an unusual marine alkaloid, isosaraine-2. Cimino, G. Fontana, A. Scognamiglio, G. and Trivellone, E. Mag. Res. Chem. 1989, 29, 327. 

Group 14 of the periodic table has generally favorable NMR properties with the exception of Ge, all elements have at least one spin 1/2 isotope of good sensitivity. Moreover, in the past years, one-dimensional (ID) and two-dimensional (2D) proton detected heteronuclear correlation NMR techniques... 

Figure 4.1 Classification of the major correlation NMR techniques used in the field of inorganic material structural characterisation. The classification has been made depending on (i) the homo- or heteronuclear, (ii) scalar or dipolar and (iii) qualitative or quantitative characteristics. Information derived from the quantitative sequences is given into brackets coupling values, d=X-Y distance and n=number of neighbours).

The first ever reported correlation NMR spectra performed with the natural abundance sensitivity of Si and presenting both types of borate units have thus been obtained by the D-HMQC technique. New insights onto the sdicate medium-range order and onto the B—Si mixing extent have been derived. Added to other correlation NMR techniques, the complete set of data gives unprecedented high detailed vision of the mixed structure of sodium boro-sdicate glass structure [67]. 

Section 13 19 2D NMR techniques are enhancements that are sometimes useful m gam mg additional structural information A H H COSY spectrum reveals which protons are spin coupled to other protons which helps m deter mining connectivity A HETCOR spectrum shows the C—H connections by correlating C and H chemical shifts... 

COSY (Section 13 19) A 2D NMR technique that correlates the chemical shifts of spin coupled nuclei COSY stands for... 

HETCOR (Section 13 19) A 2D NMR technique that correlates the H chemical shift of a proton to the chemical shift of the carbon to which it is attached HETCOR stands for heteronuclear chemical shift correlation Heteroatom (Section 1 7) An atom in an organic molecule that IS neither carbon nor hydrogen Heterocyclic compound (Section 3 15) Cyclic compound in which one or more of the atoms in the nng are elements other than carbon Heterocyclic compounds may or may not be aromatic... 

A recent series of papers [18, 24, 32-34] substantially clears up the three-dimensional polymerization mechanism in the AAm-MBAA system. Direct observation of the various types of acrylamide group consumption using NMR technique, analysis of conversion at the gel-point, and correlation of the elastic modulus with swelling indicate a considerable deviation of the system from the ideal model and a low efficiency of MBAA as a crosslinker. Most of these experimental data, however, refer to the range of heterogeneous hydrogels where swelling is not more than 80 ml ml-1 [24]. 

Polycarbonate (PC) serves as a convenient example for both, the direct determination of the distribution of correlation times and the close connection of localized motions and mechanical properties. This material shows a pronounced P-relaxation in the glassy state, but the nature of the corresponding motional mechanism was not clear 76 80> before the advent of advanced NMR techniques. Meanwhile it has been shown both from 2H NMR 17) and later from 13C NMRSI) that only the phenyl groups exhibit major mobility, consisting in 180° flips augmented by substantial small angle fluctuations about the same axis, reaching an rms amplitude of 35° at 380 K, for details see Ref. 17). 

The NMR techniques discussed so far provide information about proton-proton interactions (e.g., COSY, NOESY, SECSY, 2D y-resolved), or they allow the correlation of protons with carbons or other hetero atoms (e.g., hetero COSY, COLOC, hetero /resolved). The resulting information is very useful for structure elucidation, but it does not reveal the carbon framework of the organic molecule directly. One interesting 2D NMR experiment, INADEQUATE (Incredible Natural Abundance Double Quantum Transfer Experiment), allows the entire carbon skeleton to be deduced directly via the measurement of C- C couplings. 

One can thus safely state that NMR techniques have become flexible and valuable tools for characterizing industrial porous catalysts in length scales from nanometers to centimeters, and to correlate information on these scales, for... 

A simple NMR technique, and arguably the most widely used and effective for hit validation, is the chemical shift perturbation method. In this approach, a reference spectrum of isotopically labeled target is recorded in absence and presence of a given test ligand (or a mixture of test ligands). Commonly, differences in chemical shift between free and bound protein target are observed in 2D [15N, 1H and/or 2D [13C, H] correlation spectra of a protein (or nucleic acid) upon titration of a ligand... 

For detection of compounds in complex mixtures 2D methods are often needed. However, application of 2D correlation NMR experiments and advanced field gradient techniques is still fairly limited and awaits the possibility of quantitative evaluation. 

An astonishing number of powerful 2D and higher multidimensional NMR techniques have been developed. The common thread to all of them is to show correlations between certain nuclear properties chemical... 

Applications Useful 2D NMR experiments for identification of surfactants are homonuclear proton correlation (COSY, TOCSY) and heteronuclear proton-carbon correlation (HETCOR, HMQC) spectroscopy [200,201]. 2D NMR experiments employing proton detection can be performed in 5 to 20 min for surfactant solutions of more than 50 mM. Van Gorkum and Jensen [238] have described several 2D NMR techniques that are often used for identification and quantification of anionic surfactants. The resonance frequencies of spin-coupled nuclei are correlated and hence give detailed information on the structure of organic molecules. 

Archer SJ, Ikura M, Torchia DA, Bax A. An alternative 3D NMR technique for correlating backbone 15N with side chain H 3 resonances in larger proteins. J Magn Reson 1991 95 636-641. 

Homonuclear 19F-19F experiments are the most commonly carried out, and they are also the most easily implemented on conventional NMR spectrometers. Among such experiments, 19F COSY correlation spectroscopy is probably the 2D 19F NMR technique most frequently encountered, mainly because of through space couplings that can make it otherwise difficult to infer definitive structural information from the presence or magnitude of observed correlations. It has been found to be particularly useful in the analysis of fluoropolymers. 

In an NMR analysis of the effects of /-irradiation induced degradation on a specific polyurethane (PU) elastomer system, Maxwell and co-workers [87] used a combination of both H and 13C NMR techniques, and correlated these with mechanical properties derived from dynamic mechanical analysis (DMA). 1H NMR was used to determine spin-echo decay curves for three samples, which consisted of a control and two samples exposed to different levels of /-irradiation in air. These results were deconvoluted into three T2 components that represented T2 values which could be attributed to an interfacial domain between hard and soft segments of the PU, the PU soft segment, and the sol... 

First, 91 was subjected to a Pt02-catalyzed iminium reduction to provide the amine as a single diastereomer (94, 83 %, Scheme 6.16). At this point 2D NMR techniques more clearly highlighted the correlations with the new me thine adjacent... 

The development and application of multidimensional solid state homo- and heteronuclear correlation (HETCOR) NMR techniques have lead to an increasingly important role in structure solution of zeolitic materials and have had many practical applications in the detailed structural characterization of completely siliceous zeolites[6,7] and AlPOs.[8-ll] However, HETCOR NMR is not readily applicable to aluminosilicates... 

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