Chemical shift correlations carbon

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... 

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... 

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. 

NMR chemical shift data from die protons ortho or para to the electron-withdrawing group can be used to determine the reactivity of the monomer indirecdy.58 Carbon-13 and 19F NMR can be used to probe the chemical shift at the actual site of nucleophilic reaction. In general, lower chemical shifts correlate widi lower monomer reactivity. Carter reported that a compound might be appropriate for nucleophilic displacement if the 13 C chemical shift of an activated Buoride ranges from 164.5 to 166.2 ppm in CDC1359. 

Like the HMBC, the COLOC experiment provides long-range hetero-nuclear chemical shift correlations. The COLOC spectrum, H-NMR, and C-NMR data of 7-hydroxyfrullanolide are presented here. Use the data to assign the quaternary carbons. 

Ionic dissociation of carbon-carbon a-bonds in hydrocarbons and the formation of authentic hydrocarbon salts, 30, 173 Ionization potentials, 4, 31 Ion-pairing effects in carbanion reactions, 15, 153 Ions, organic, charge density-NMR chemical shift correlations, 11,125 Isomerization, permutational, of pentavalent phosphorus compounds, 9, 25 Isotope effects, hydrogen, in aromatic substitution reactions, 2,163... 

Zheng et al. [1] postulated that the driving force for placing Zr and B on the same carbon might stem from interactions between the zirconium and oxygen or boron and chlorine atoms. However, an X-ray analysis of 22 revealed that there are no intra- or intermo-lecular interactions between any of these atoms [35]. Compound 22 was also unambiguously characterized by 1H-1H double quantum filtered COSY [36] and 13C-1H heteronuc-lear chemical shift correlation NMR spectroscopy [37,38]. Considerable differences in the chemical shifts of the diastereotopic Cp groups were found in both the XH and 13C NMR spectra. The NMR study unequivocally showed that the methine proton was at-... 

NMR spectra of solids, and thus soil, are obtained by what is called magic angle spinning. The spectra obtained have broader absorption features than NMR spectra of components in solution or liquids. Numerous NMR experiments such as 3H—13C heteronuclear chemical shift correlation (HETCOR), which identifies which hydrogen atoms are attached to which carbon atoms, can also be carried out on solid samples. A great deal of useful information about the structure of components in soil can thus be obtained from NMR investigations [5,6],... 

Figure 7. Correlation of corrected proton chemical shifts with carbon-13 chemical shifts. See Table 1.

Substitution of heteroatoms on carbonium ion centres often has a profound and unexpected effect on the carbon-13 chemical shift which is hardly designed to bolster our confidence in the simplicity of the charge density-chemical shift correlation. A few examples will illustrate the point (in the following structures carbon-13 shifts are given in regular type, proton shifts in italics). 

The dramatic effect of nitrogen substitution on carbon-13 chemical shifts was illustrated at the beginning of this section by the fact that the a/p/ia-carbon resonance of pyridine moves upheld upon protonation at nitrogen. A further demonstration that nitrogen substitution does still more extensive violence to charge density-chemical shift correlations is seen in Figures 19 and 20. Thus, in... 

The order in which various NMR data are acquired is largely one of user preference. Acquisition of the proton reference spectrum will invariably be undertaken first. Whether a user next seeks to establish homo- or heteronuclear shift correlations is where individual preferences come into play. Many spectro-scopists proceed from the proton reference spectrum to either a COSY or a TOCS Y spectrum next, while others may prefer to establish direct proton-carbon chemical shift correlations. This author s preference is for the latter approach. From a multiplicity-edited HSQC spectrum you obtain not only the carbon chemical shifts, which give an indication of the location of heteroatoms, the degree of unsaturation and the like, but also the number of directly attached protons, which eliminates the need for the acquisition of a DEPT spectrum [51, 52]. The statement in the prior sentence presupposes, of course, that there the sensitivity losses associated with the acquisition of multiplicity-edited HSQC data are tolerable. 

Generally, 13C chemical shifts correlate with some typical properties of carbon within its molecular environment discussed in the following sections. 

A second difficulty of fully decoupled 13C NMR spectra is that die connectivity in the molecule is difficult to establish (except by chemical shift correlation) because coupling patterns are absent. This dilemma is partially resolved by die use of a technique called off-resonance decoupling. In off-resonance decoupled 13C spectra, the carbons are coupled only to diose protons directly attached to diem and die coupling is first order. Thus quaternary carbons are singlets, methine carbons are doublets, methylene carbons are triplets, and methyl carbons are quartets. It is possible to use diis information to establish proton-carbon connectivity,... 

Variable temperature 13C H NMR studies on 45 show large coupling of the a-carbon atoms of the metallacyclopentane ring to the 183W nucleus (70 and 86 Hz), in contrast to the smaller coupling associated with the coordinated ethene (33 and 37 Hz). A two-dimensional 13C NMR shift correlation study confirmed the connectivity observed in the X-ray study, while 13C 111 chemical shift correlation experiments identified the H NMR resonances. 

The partial long range C-H chemical shift correlation spectrum presented in figure 3 shows signals from the aliphatic side chains of the trimeric compound. This 2-D NMR experiment provides information about the H-C connection 2 to 3 bonds away from the carbon (coupling constants less than 20 Hz). For example, Ha shows... 

Figure 9.6 shows a 2D HETCOR spectrum with the ID 13C spectrum displayed at the top (horizontal or F2 dimension) and the ID lH spectrum displayed vertically on the left side (vertical or Fi dimension). From any peak (resonance) in the lH spectrum, we can follow a horizontal line until we encounter a spot or blob of intensity in the 2D data matrix. These clusters of intensity represent correlations in the 2D spectrum and are called crosspeaks. From the crosspeak we move up along a vertical line and run into the 13C peak in the ID 13C spectrum corresponding to that proton s personal carbon atom (the one it is directly bonded to). In this way we can pair up each proton peak in the lH spectrum with a carbon peak in the 13C spectrum—a process called chemical-shift correlation. 

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