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NOESY, Nuclear Overhauser Enhancement Spectroscopy

Figure 3.1 The various time periods in a two-dimensional NMR experiment. Nuclei are allowed to approach a state of thermal equilibrium during the preparation period before the first pulse is applied. This pulse disturbs the equilibrium ptolariza-tion state established during the preparation period, and during the subsequent evolution period the nuclei may be subjected to the influence of other, neighboring spins. If the amplitudes of the nuclei are modulated by the chemical shifts of the nuclei to which they are coupled, 2D-shift-correlated spectra are obtained. On the other hand, if their amplitudes are modulated by the coupling frequencies, then 2D /-resolved spectra result. The evolution period may be followed by a mixing period A, as in Nuclear Overhauser Enhancement Spectroscopy (NOESY) or 2D exchange spectra. The mixing period is followed by the second evolution (detection) period) ij. Figure 3.1 The various time periods in a two-dimensional NMR experiment. Nuclei are allowed to approach a state of thermal equilibrium during the preparation period before the first pulse is applied. This pulse disturbs the equilibrium ptolariza-tion state established during the preparation period, and during the subsequent evolution period the nuclei may be subjected to the influence of other, neighboring spins. If the amplitudes of the nuclei are modulated by the chemical shifts of the nuclei to which they are coupled, 2D-shift-correlated spectra are obtained. On the other hand, if their amplitudes are modulated by the coupling frequencies, then 2D /-resolved spectra result. The evolution period may be followed by a mixing period A, as in Nuclear Overhauser Enhancement Spectroscopy (NOESY) or 2D exchange spectra. The mixing period is followed by the second evolution (detection) period) ij.
Nuclear Overhauser enhancement spectroscopy (NOESY) experiments play a very important role in structural studies in quinolizidine derivatives. For instance, the endo-type structure of compound 28 was proven by the steric proximity of the H-3a and H-12a protons according to the NOESY cross peak, while the spatial proximity of the H-6f3 and H-8/3 protons reveals that tha A/B ring junction has a /ra t-stereochemistry. Similarly, compound 28 could be distinguished from its regioisomer 29 on the basis of the NOESY behavior of its H-13 atom <1999JST153>. [Pg.7]

The relative stereochemistry of hyperaspine 93 was determined by 2-D NMR spectroscopic and mass spectrometry (MS) methods. It has a m-fused bicyclic conformation 93a <2001TL4621>. The trans-fused one is disfavored by an axial pentyl group at C-8 and by a destabilizing dipole-dipole interaction between the N- and O-atoms, which does not exist in the alternative //.(-conformation. The geminal coupling constant of C( 1 )H2 in 93 (11.0 Hz), and that of its 6-hydroxy derivative (11.2 Hz), indicates that they exist preferentially in / //-conformations, whereas their 6-epimers adopt trans-conformations (9.3 and 8.4 Hz, respectively) <2005EJ01378>. Nuclear Overhauser enhancement spectroscopy (NOESY) studies also confirmed the stereochemistry of 93 by the marked nuclear Overhauser effect (NOE) correlation between H-3 and H-4a <20030L5063>. [Pg.94]

Assignment of the isotropically shifted signals observed for the CuNiSOD example discussed in the previous paragraph has been achieved by means of anion titrations (not discussed here) and nuclear Overhauser enhancement spectroscopy (NOESY), to be discussed next. In Figure 3.24B the CuNiSOD active site is depicted with histidine nitrogens and protons identified for the discussion of the NOESY results. The copper(II) ion is coordinated to the N ligand atoms of his46... [Pg.112]

The stereochemistry of the obtained acetals was confirmed by nuclear overhauser enhancement spectroscopy (NOESY) measnrement in NMR spectra. [Pg.97]

Aryl derivatives of thieno[3,2-f]pyridines, 36 and 37, have been the subject of two-dimensional (2-D) NMR studies. Phase-sensitive nuclear Overhauser enhancement spectroscopy (NOESY) and correlation spectroscopy (COSY) experiments confirm the nonplanar conformation of the two aromatic ring systems <1999SAA1035>. [Pg.273]

The spirobenzoxazepine 28 was studied by 2-D and nuclear Overhauser enhancement Spectroscopy (NOESY) NMR and X-ray crystallography, and in both cases the same chair conformation, 28, was formed (See Figure 5). The authors conclude that this compound 28 is a semirigid scaffold, able to present various substituents without undergoing hydrophobic collapse, and 28 behaves structurally as a privileged structure <2004TL1051>. [Pg.259]

Correlation spectroscopy (COSY), nuclear overhauser enhancement spectroscopy (NOESY), I-D NOE, and HPLC techniques were utilized in the identification of three trapped products formed from coupling of the generated C4-centered radical of artemisinin with manganese(n) tetraphenylporphorin <2001AGE1954>. [Pg.302]

H and 13C NMR techniques have widely been used to determine the configuration of new dioxepins and dithiepins and to elucidate the constitution and conformation of new naturally occurring substances. For example, the configuration of oximes 14 was determined by H and 13C correlated spectra, correlation spectroscopy (COSY), nuclear Overhauser enhancement spectroscopy (NOESY), heteronuclear correlation (HETCOR) spectroscopy, and hetero-nuclear multiple bond correlation (E1MBC) spectroscopy <1998CCA557>. [Pg.324]

A novel cysteine derivative, spongiacysteine, was isolated recently from marine sponge. It was converted to lactone 4 by reaction with 2,4,6-trichlorobenzoyl chloride, 4-dimethylaminopyridine (DMAP), and triethylamine. Selected nuclear Overhauser enhancement spectroscopy (NOESY) correlation and coupling constants are given <2004CL1262>. [Pg.369]

Notably, two isomeric products can be generated. The usual infrared (IR) and mass spectra as well as H and 13C NMR chemical shifts could not define which isomer was formed. The authors used different NMR techniques, such as 2-D heteronuclear multiple bond correlation (HMBC) experiments and phase-sensitive nuclear overhauser enhancement spectroscopy (NOESY) measurements to elucidate the product s structure. [Pg.408]

The vast literature associated with flavanoid chemistry precludes a discussion here but two valuable reviews have been published. The first reviews a number of spectroscopic techniques used for flavonoid analysis, with a strong emphasis on NMR spectroscopy (plus also mass spectrometry, vibrational spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, X-ray crystallography, and circular dichrosim (CD)) . The second review deals with NMR methods that have been successful in the characterization of phenolic acids and flavonoids from plant extracts that have not been separated or isolated as single components. The emphasis of the article is 2-D NMR methodology and a variety of experiments such as total correlated spectroscopy (TOCSY), COSY, nuclear Overhauser enhancement spectroscopy (NOESY) and heteronuclear multiple quantum correlation (HMQC) are discussed . [Pg.343]

Laurie was one of the first to apply two-dimensional (2D) NMR to carbohydrates. With students Subramaniam Sukumar and Michael Bernstein, and visiting scientist Gareth Morris, he demonstrated and extended the application of many of the directly observed 2D NMR techniques of the time. These included the homo- and hetero-nuclear 2D /-resolved techniques, delayed proton /-resolved NMR that allowed broad resonances to be suppressed, for example, those of dextran in the presence of methyl /Lxvlopyranoside. proton-proton chemical shift correlation spectroscopy (COSY), nuclear Overhauser enhancement spectroscopy (NOESY), proton-carbon chemical shift correlation (known later as HETCOR), and spin-echo correlated spectroscopy (SECSY). Trideuteriomethyl 2,3,4,6-tetrakis-<9-trideuterioacetyl-a-D-glucopyranoside served as a commonly used model compound for these studies. [Pg.30]

Intramolecular dynamics of 1,5-dihydronaphtho[l,8-(s/][l,2,3]trithiocine 16 in solutions was studied by 2-D nuclear Overhauser enhancement spectroscopy (NOESY) technique <2003AMR97> and interpreted based on the... [Pg.480]

Consecutive nuclear Overhauser enhancement spectroscopy (NOESY) experiments allowed one to calculate the distance between the enolate proton and other protons in the octahedrally coordinated titanium enolate 13. The H -tf and H -H- distances calculated from NMR spectra are 0.2 A longer or 0.5 A shorter, respectively, than those in the model structures. Using modeling studies, the same prediction can be observed, indicating that one side of the Ti enolate complex is less sterically hindered than the other side. This is due to the efficient diffusion pathway formed by the enolate H (H ), the protons on the i-Pr group (H, Me) and the protons on the selone heterocycle (H, H ). These distances confirm that the enolate oxygen atoms are cis to each other and their orientation should promote a strong facial preference upon subsequent reaction with an aldehyde or ketone. [Pg.118]

The stereochemistry of compounds 60-63 was fully determined by various NMR techniques such as nuclear Overhauser effect (NOE), correlation spectroscopy (COSY), and nuclear Overhauser enhancement spectroscopy (NOESY) <1996MRC52>. The conformation of the 2,3-butanedione trimer 64 and similar compounds has been examined by NMR at —90°C <2000T10005>. [Pg.845]

The favored conformations of ABA and analogs 20-23 were examined by NMR and computer-aided calculations [54]. Some NOEs were observed in the NOE difference spectra and nuclear Overhauser enhancement spectroscopy (NOESY) (data not shown). However, the NOE is difficult to be a decisive evidence for the lowest-energy-... [Pg.337]


See other pages where NOESY, Nuclear Overhauser Enhancement Spectroscopy is mentioned: [Pg.152]    [Pg.983]    [Pg.401]    [Pg.53]    [Pg.316]    [Pg.704]    [Pg.41]    [Pg.210]    [Pg.547]    [Pg.1236]    [Pg.458]    [Pg.122]    [Pg.697]    [Pg.821]    [Pg.3]    [Pg.122]    [Pg.718]    [Pg.177]    [Pg.12]    [Pg.652]    [Pg.148]    [Pg.281]    [Pg.158]    [Pg.108]    [Pg.152]    [Pg.100]   
See also in sourсe #XX -- [ Pg.2 , Pg.110 , Pg.173 , Pg.288 ]

See also in sourсe #XX -- [ Pg.99 ]




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