Chemical shift data

Nuclear magnetic resonance (NMR) spectroscopy is the most powerful spectroscopic method for structural elucidation of organic molecules and is routinely used by organic chemists. Summarised below are common NMR active nuclei chemical shift data for NMR solvents, common impurities, and functional groups coupling constants and details of common NMR experiments used to determine the connectivity and stereochemistry of small organic molecules. 

These are listed in Table 12.6, along with details on NMR frequency and isotopic abundance. 

Chemical Shift Data for Residual Protons in Common NMR Solvents 

Organic Chemist s Desk Reference, Second Edition 

Chemical Shift Data for Common Solvents and Impurities in CDCI3 

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The H NMR spectra of formic acid (HCO2H) maleic acid cis H02CCH=CHC02H) and malonic acid (HO2CCH2CO2H) are similar in that each is charactenzed by two singlets of equal intensity Match these compounds with the designations A B and C on the basis of the appro pnate H NMR chemical shift data... 

Proton chemical shift data from nuclear magnetic resonance has historically not been very informative because the methylene groups in the hydrocarbon chain are not easily differentiated. However, this can be turned to advantage if a polar group is present on the side chain causing the shift of adjacent hydrogens downfteld. High resolution C-nmr has been able to determine position and stereochemistry of double bonds in the fatty acid chain (62). Broad band nmr has also been shown useful for determination of soHd fat content. 

The NMR spectra of heterocyclic compounds with seven or more ring members are as diverse as the shape, size and degree of unsaturation of the compounds. NMR is perhaps the most important physical method to ascertain the structure, especially the conformational statics and dynamics, of large heterocycles. Proton-proton coupling constants provide a wealth of data on the shape of the molecules, while chemical shift data, heteroatom-proton coupling constants and heteronuclear spectra give information of the electronic structure. Details are found in Chapters 5.16-5.22. Some data on seven-membered rings are included in Table 10. 

The order of enolate reactivity also depends on the metal cation which is present. The general order is BrMg < Li < Na < K. This order, too, is in the order of greater dissociation of the enolate-cation ion pairs and ion aggregates. Carbon-13 chemical shift data provide an indication of electron density at the nucleophilic caibon in enolates. These shifts have been found to be both cation-dependent and solvent-dependent. Apparent electron density increases in the order > Na > Li and THF/HMPA > DME > THF >ether. There is a good correlation with observed reactivity under the corresponding conditions. 

It is evident from Table 2 that the chemical shift data are very similar in both states of aggregation. Only the carbonyl carbon show a small but definite shifts, 2 ppm. In the solution state, in acetone -d6 solution the relaxation times T1 of the pyranose carbon atoms are very similar and only slightly smaller than those of the carbon atom of the methyl group in the acetyl substituent, while the T1-value of the carbon atom of the carbonyl group is considerably higher. 

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. 

The TioRio compounds are generally air-stable white solids and their physical properties are similar in many ways to their TsRs counterparts although much fewer data are available. The Si NMR chemical shift data for a range of TiqRio compounds are given in Table 36, data for compounds containing more than one... 

The only physical property which has been studied for substituted vinylidene sets is the nmr chemical shift of the vinylidene proton in substituted ethylenes and in tra s-l,2-disubstituted ethylenes. The first attempt at correlating chemical shift data for substituted ethylenes with the Hammett equation appears to be the work of Banwell and Sheppard (53), who reported a correlation of A2 values with the or constants, the A2 values being defined by the equation... 

Eleven sets of chemical shift data were correlated with eq. (2). The sets studied are shown in Table V, and the results of the correlations are reported in Table VI. Only in one set were the results significant (set 5-12), and even in this set, correlation was very poor. It seems certain that no meaningful relationship... 

Selected, C-N.m.r., Chemical-shift Data" for Giycopentapeptide 10 and Its Reductively C]Methylated Derivative ... 

Chemical-shift Data and Titration Data" for the N-Terminal Di[ C]methylamino Groups of Glycophorins, Glycophorin Glycopeptides, and Related Peptides and Glycopeptides... 

C Chemical-shift Data and Titration Data for the N-Terminal Mono( C)methyIamino Groups of Glycophorin-related Glycopeptides and Peptides ... 

Together with this kind of information and the chemical-shift data presented in Table I, the information gathered agrees well with structure 10. 

C-N.m.r. Chemical-shift Data for Various a- and /J-D-Glycosyl-L-serine Derivatives... 

In the literature, the anomeric configuration of the carbohydrates has usually been deduced from the C-l chemical-shift and from the spectral pattern, if observable. Because relevant model compounds were not previously available for providing C-l chemical-shift data for glycopep-... 

C-N.m.r. Chemical-shift Data for the Anomeric-Carbon Atoms and C, and Coupling Constants ( /ch) Measured for Selected Gland /S-D-Glycosyl-L-threonine Model Compounds19- 1,82-84... 

The results of study of the chemical-shift data for these large numbers... 

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