HETCOR spectra

COSY and HETCOR experiments are extremely useful in the structure elucidation of complex organic molecules. The geminal and vicinal protons and their one-bond C-H connectivities are first identified from the HETCOR spectrum, and then the geminal couplings are eliminated from the COSYspectrum, leaving vicinal connectivities. By careful interpretation of the COSY and the one-bond HETCOR spectra, it is then possible to obtain information about the carbon-carbon connectivities of the protonated carbons ( pseudo-INADEQUATE information). In this way the carbon-carbon connectivity information of protonated carbons is obtainable through a combination of COSY and HETCOR experiments. 

The proton NMR spectrum of miconazole nitrate was obtained using a Bruker Instrument operating at 300, 400, or 500 MHz. Standard Bruker Software was used to execute the recording of DEPT, COSY, and HETCOR spectra. The sample was dissolved in DMSO-d6 and all resonance bands were referenced to the tetramethyl-silane (TMS) internal standard. The 1H NMR spectra of miconazole nitrate are shown in Figs. 5-7 and the COSY 1H NMR spectrum is shown in Fig. 8. The H NMR assignments for miconazole nitrate are provided in Table 3. 

The proton nuclear magnetic resonance (NMR) spectrum of valproic acid was obtained using a Bruker Avance Instrument operating at 300, 400, and 500 MHz. Standard Bruker Software was used to obtain COSY and HETCOR spectra. The... 

The capabilities of some of these schemes are shown in Fig. 20, featuring a series of 2D 27A1-31P HETCOR spectra of A1P04-14, including 27A1 31P R-INEPT (MAS-based, acquired at 9.4 T and 18.8 T), [31P]27A1 HMQC (following the approach of Massiot et al. [254], also acquired at 9.4 T and 18.8 T), as well as... 

Fig. 20 2D HETCOR spectra of A1P04-14 (a) 27A1 31P R-INEPT at 9.4 T, (b) 27A1 31P HMQC at 9.4 T, (c) 27A1 31P R-INEPT at 18.8 T, (d) 27A1 31P HMQC at 18.8 T, (e) 27A1 31P SPAM-MQ-/-HETCOR with R-INEPT at 18.8 T, and (f) 27AI 3IP SPAM-MQ-D-HETCOR obtained using cross-polarization at 18.8 T. The total experimental times were 5 h (a), 5 h (b), 2 h (c), 2 h (d), 10 h (e) and 7 h (f). (Reproduced with permission from [235])...

Information about the surface and interface structures in hexadecylamine-capped CdSe NC of 2 nm size has been obtained by a variety of 1H, 13C, 113Cd, and 77Se NMR techniques [342]. The 77Se CP-MAS-NMR spectrum showed five partially resolved peaks from surface or near-surface Se environments. It was possible to obtain 2D heteronuclear correlation (HETCOR) spectra between 1H and the other three nuclei despite the inherent sensitivity limitations (the 77Se- 3I-I HETCOR experiment required 504 h ). The latter experiment indicated that the methylene protons of the hexadecylamine chain interact with the surface Se atoms via a tilt of the chain toward the surface. The surface Se atoms were not seen to interact with thiophenol present, and it was suggested that thiophenol binds to a selenium vacancy at the surface. 

In kaplanin, the p configuration of the sugar in the 5-hydroxy-7-methoxy-8-C-p-glucosyl-flavone was indicated by H NMR and supported by H- H COSY. H and C NMR and HETCOR spectra gave the precise location of the glucose moiety. 

Fig. 21. The 2D FSLG 13C- H HETCOR spectra of PG/PLY (50/50) blend sample with contact time of 0.2 ms.

Fig. 24. Expanded 2D FSLG 13C-H HETCOR spectra for the carbonyl carbon...

The correlation signals between PG and PLV corresponding to an intermolecular distance less than 4 A are observed in the FSLG l3C ll HETCOR spectra with a contact time of 0.5 ms. Further, the correlation signals between PG (Ha) and the side chain of PLV (Cy) are observed only in the FSLG 13C- H HETCOR spectra with a long contact time of... 

Fig. 25. One-dimensional slices along the horizontal axis of the 2D FSLG C H HETCOR spectra taken at (a) 4.7 ppm (PG (P) Ha) and (b) 9.3 ppm (PG (P) HN) on the H chemical shift axis.The contact time used in this experiment 1.5, 0.5 and 0.2 ms.

The relationship between intra- and intermolecular correlation signals from the 2D FSLG 13C-3H HETCOR spectra and carbon-proton distances from the modeled structure is shown in Table 15. 

Figure 18 Comparison of (a) z-filtered and (b) the ordinary correlated, INEPT based, 2D HETCOR spectra of Me3SiC(0)CH3...

Figure 3.25. Na- P 2D HETCOR spectra of Na3P309 A. Obtained with the normal HETCOR pulse sequence and B. with MQ-MAS incorporated in the pulse sequence to obtain higher resolution from Wang, De Paul and Bull (1997) with permission of the copyright owner.

To keep experimental times and data storage requirements reasonable, far fewer data points are used in each dimension in 2D experiments than with typical ID experiments. Reasonable digital resolution can be obtained in the detected dimension (02) for H, homonuclear correlation (e.g., COSY) and H-detected, heteronuclear correlation (e.g., HMQC) spectra by using 1,024 or 2,048 data points. Due to their greater spectral widths, however, heteronuclear-detected correlation (e.g., HETCOR) spectra require 2,048, or even 4,096, data points in U2. 2D experiments are commonly performed with 2,048 data points in each dimension. 

Figure 13. Pulse sequence and coherence transfer pathway diagram for the REPT-HSQC heteronuclear ( H- 13C) experiment, which is suitable for recording HETCOR spectra. Dark- and light-shaded rectangular blocks represent rf pulses of flip angle 90° and 180°, respectively. For more details, see ref 125.

Figure 14. A comparison of three HETCOR spectra of naturally abundant L tyrosine-HCI recorded under as far as possible equivalent conditions using (a) the FSLG-decoupled CP (Figure 11), (b) the MAS / HMQC (Figure 12), and (c) the REPT-HSQC (Figure 13) experiments. Above each spectrum, the 13C skyline projection as well as the Fourier transformation of the first slice (q = 0) of the 2D data set is shown, while below each spectrum the 11 i skyline projections are shown. The spectra were recorded at a H Larmor frequency of 500 MHz the improvement in resolution at a Larmor frequency of 700 MHz for the REPT-HSQC experiment is shown as a dashed line. (Reproduced with permission from ref 125. Copyright 2001 Academic Press.)...

H-13C HETCOR spectra obtained for a sample of L-tyrosine-HCl at a H Larmor frequency of 500 MHz using the FSLG-decoupled CP (Figure 11), the MAS-J-HMQC (Figure 12), and the REPT-HSQC (Figure... 

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