HETCOR Correlation

Figure 2.10 (a) 2D H- N HETCOR correlation spectrum of fully N-labeled complex [(=SiO)2Ta(=NH) (NHj)] and [=Si- NH2] and comparison with 2D double quantum (b) and triple quantum (c) correlation spectra. An exponential line broadening of 100 Hz was applied to all the proton dimensions before Fourier transform. The dotted gray lines correspond to the resonances of the tantalum NH, NH2 and NH3 protons. The dotted circles underline the absence of auto-correlation peaks for the imido proton in the double quantum spectrum (b), and for the amido proton in the triple quantum, spectrum (c) (from Reference [9]). 

Table 15. Observed 2D FSLG 13C-H HETCOR correlation peaks of PG/PLY (50/50) blend sample and calculated carbon-proton distances for antiparallel P-sheet for the PG-PLY...

Very recently, an interesting modification of HETCOR correlation was published by Chan and co-workers.69 In this experiment, a DQ filter is incorporated into the pulse sequence of HETCOR spectroscopy so that a DQ excitation profile can be obtained by measuring a series of 2D spectra (Figure 14). This method offers a simple experimental approach to extract the van Vleck second moment of a multiple-spin system under high-resolution condition. Hydroxyapatite (Ca10(PO4)6(OH)2) and brushite (CaHP04 2H20) were used as reference samples. 

Unfortunately, so far, there are no reports showing applications of 1H-31P or 31P-1H HETCOR correlations under ultra-fast MAS in structural studies of phosphorus compounds but, for sure, this approach traces the future for HETCORs. 

HETCOR correlates all proton resonances to those of the corresponding carbons and can be used to determine interglycosidic linkage, taking into account the known glycosidation shifts. 

COSY rmd HOHAHA revealed spin correlations for rhamnose and glucose units between each pair from H-1 to H-6, and for arabinose between each pair from H-1 to H-4. The coherence transfer to methylene H-5 of arabinose is not observable because of the small Jh4-H5- HETCOR correlating all proton resonances to those of the corresponding carbons, gives the position of the interglycosidic linkages. Thus two sequence are possible ... 

HETCOR Correlating coupled heteronuclear spins across a single bond. Employs detection of the lower-7 nuclide, typically C, so has... 

Figure 3 (A) Schematic representation of a Cs z-PDI molecule with color-coding matching the assignment based on (B) a 2D C H -FSLG-HETCOR correlation spectrum using a ramped CP transfer of 500 ps. The asterisks indicate an artifact from the transmitter (in the middle of the 2D spectrum) and spinning side bands. (C) The experimental Hbr-Hbr DQ sideband pattern is extracted from a 2D DQ-SQ H- H correlation spectrum based on 8 rotor periods of DQ recoupling obtained at 25.0 kHz MAS with the dwell time set to 2.0 ps in the indirect dimension. The Hb- Hbr DQ sideband pattern shows significant two-spin correlation, and the Hb- Hb, intermolecular distance is estimated to be 3.7 0.1 A. All experiments were acquired at 20.0 T. Adapted with permission from Ref [86], Copyright 2009 American Chemicai Society.

A second 2D NMR method called HETCOR (heteronuclear chemical shift correlation) is a type of COSY in which the two frequency axes are the chemical shifts for different nuclei usually H and With HETCOR it is possible to relate a peak m a C spectrum to the H signal of the protons attached to that carbon As we did with COSY we 11 use 2 hexanone to illustrate the technique... 

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... 

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... 

Heteronuclear chemical shift-correlated spectroscopy, commonly called H-X COSY or HETCOR has, as the name implies, different and F frequencies. The experiment uses polarization transfer from the nuclei to the C or X nuclei which increases the SNR. Additionally, the repetition rate can be set to 1—3 of the rather than the longer C. Using the standard C COSY, the ampHtude of the C signals are modulated by the... 

CH COSY Correlation via one-bond CH coupling, also referred to as HETCOR (heteronuclear shift correlation), provides carbon-13- and proton shifts of nuclei in C//bonds as cross signals in a 5c versus 8h diagram, assigns all C//bonds of the sample... 

HETCOR (Section 13.19) A 2D NMR technique that correlates the H chemical shift of a proton to the C chemical shift of the carbon to which it is attached. HETCOR stands for heteronuclear chemical shift correlation. 

The basic pulse sequence employed in the heteronuclear 2D shift-correlation (or HETCOR) experiment is shown in Fig. 5.40. The first 90° H pulse bends the H magnetization to the y -axis. During the subsequent evolution period this magnetization processes in the x y -plane. It may be considered to be made up of two vectors corresponding to the lower (a) and higher (/3) spin states of carbon to which H is coupled. These two... 

The HETCOR spectrum of a naturally occurring isoprenylcoumarin is shown in Fig. 5.41. The spectrum displays one-bond heteronuclear correlations of all protonated carbons. These correlations can easily be determined by drawing vertical and horizontal lines starting from each peak. For example, peak A represents the correlation between a proton resonating at 8 1.9 and the carbon at 8 18.0. Similarly, cross-peaks E and F show that the protons at 8 4.9 and 5.1 are coupled to the same carbon, which resonates at 8 114.4 i.e., these are the nonequivalent protons of an exomethylenic... 

Figure 5.41 Heteronuclear shift correlation (HETCOR) spectrum of an isoprenyl-coumarin.

H/ C One-Bond Shift Correlations by Hetero-COSY (HETCOR) Experiment... 

The one-bond HETCOR spectrum and C-NMR data of podophyllo-toxin are shown. The one-bond heteronuclear shift correlations can readily be made from the HETCOR spectrum by locating the posidons of the cross-peaks and the corresponding 5h and 8c chemical shift values. The H-NMR chemical shifts are labeled on the structure. Assign the C-NMR resonances to the various protonated carbons based on the heteronuclear correlations in the HETCOR spectrum. 

Heteronuclear correlation spectroscopy (HETCOR) Shift-correlation spectroscopy in which the chemical shifts of different types of nuclei (e.g., H and C) are correlated through their mutual spin-coupling effects. These correlations may be over one bond or over several bonds. 

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. 

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