2D-COSY

Figure 1.45 Coherence transfer pathways in 2D NMR experiments. (A) Pathways in homonuclear 2D correlation spectroscopy. The first 90° pulse excites singlequantum coherence of order p= . The second mixing pulse of angle /3 converts the coherence into detectable magnetization (p= —1). (Bra) Coherence transfer pathways in NOESY/2D exchange spectroscopy (B b) relayed COSY (B c) doublequantum spectroscopy (B d) 2D COSY with double-quantum filter (t = 0). The pathways shown in (B a,b, and d) involve a fixed mixing interval (t ). (Reprinted from G. Bodenhausen et al, J. Magn. Resonance, 58, 370, copyright 1984, Rights and Permission Department, Academic Press Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887.)...

Gelsevirine (2) was first isolated in 1953 from G. sempervirens as a minor component (3). Its structure was later elucidated on the basis of mass spectrometry as well as H-NMR and 13C-NMR studies (4). Gelsevirine has been found to be the predominant alkaloid in G. rankinii (24), and it was claimed that some of the previously reported 1 H-NMR and 13C-NMR data should be revised. Thus the previous assignments of H-16, H-15, H-14a, H-14e, and H-6 for gelsevirine should be changed to H-15, H-14a, H-16, H-6, and H-14e, respectively, from the evidence of the more accurate homonu-clear 2D COSY experiments. Similarly, from the heteronuclear 2D correlation spectrum, the assignments for C-16, C-15, C-6, and 1V-CH3 should be revised to C-15, C-16,1V-CH3, and C-6, respectively. 

The proton assignments of H-17e, H-17a, H-6a, and H-6e are made by examination of the dihedral angles with Dreiding models and the J values. These and the other proton assignments are confirmed by 2D COSY experiments. 

The relative configurations and predominant conformations of [l,2,3]oxathiazino[4,3- ]isoquinoline derivatives 177-182 were studied by means of H and 13C NMR spectroscopy with the applications of DNOE, 2D HSC, and 2D-COSY measurements. Their stereostructure includes an equilibrium between the conformers cis-1, trans and cis-2. In the /ra -structure, the B/C rings are trans-ane-WatcA with H-l lb and the N-5 lone electron pair trans-diaxial. In the cis structures, the hetero-rings are air-anellated in the cis-1 conformation C-l is in inside position, while in cis-2... 

Figure 12 2D-COSY-45 NMR spectrum (400,13 MHz) of 3-endo-silylbicyclobutonium ion 40 (SiR3 = Si(Me) -Bu) in S02CIF/S02F2 at -112 °C, int. ref TMA S(N(Me)/) 55.65 ppm. Cross peaks between Ha and Hrare...

For the new C-hydroxybenzyl glycoflavones from Citnillus colocynthis," the complete C NMR data were assigned and additionally confirmed by 2D-COSY, HETCOR, and selective INEPT experiments. 

C This pulse sequence, the popular homonuclear 2D COSY (COrelation Speciro-scopY) experiment, was designed to determine the entire H/ H-coupling network of a molecule within a single experiment. The sequence consist of all four elements, i.e. a preparation, a evolution, a mixing and a detection period. The evolution period serves to introduce the second time (tl) domain of a 2D experiment and in the mixing period, which is actually a pulse, polarizations are exchanged among the coupled spins. 

TOCSY spectra usually give no information about direct coupling interactions and hence details of J-coupling networks. This missing information is commonly obtained either from ID homodecoupling or more efficiently from 2D COSY spectra. 

Load the 2D COSY (magnitude mode) spectrum of peracetylated glucose D NMRDATA GLUCOSE 2D HH GHHCO 001999.RR. The 2D spectrum appears in the default contour display mode and shows only positive cross peaks. Use the mouse to select a suitable expansion. 

Load the phase sensitive 2D COSY spectrum of peracetylated glucose... 

Try out the effect of several modes for DC correction available with 2D data. Load the raw data of the magnitude mode 2D COSY spectrum D NMRDATA GLUCOSE 2D HH GHHCO 001001.SER and choose no, quad and qpol as BC mod in F2. Note that usually for Fl no baseline correction is applied in the time-domain, i.e. BC mod (F1) = no. Fourier transform the data and store the individual spectra using ascending processing numbers. Compare corresponding rows to inspect the effect of different baseline corrections. 

The acquisition of a two-dimensional (2D) NMR spectrum gives the advantage of obtaining information about both the chemical shifts values 8 and the coupling system of each proton (the 2D plot allows us to establish the assignments of such coupling systems). Figure 5.2.5 depicts the stopped-flow 2D COSY NMR spectrum of all-E lycopene from a tomato extract. This was recorded within 24 h with a total of 280 increments and 256 transients. 

Figure 8.2.8 Two-dimensional sub-spectra generated from the original and gradient-shifted 2D-COSY spectra of four coils using the subtraction method and nulling of the diagonal peaks (a) 1-propanol (b) ethanol. Reprinted from Hou, T., MacNamara, E. and Raftery, D., NMR analysis of multiple samples using parallel coils improved performance using reference deconvolution and multidimensional methods , Anal. Chem. Acta, 400, 297-305, copyright (1999), with permission of Elsevier Science...

The analysis of 2D COSY and NOESY NMR spectra of the PCA products showed the presence of two isomeric crown-containing cyclobutane derivatives 7a and 7b in 17 83 ratio (Scheme 8). 

Homonuclear decoupling is pretty much a historical experiment, as newer experiments such as 1D-TOCSY (Chapter 8) and 2D-COSY (Chapter 9) have replaced it. 

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