Chemical shift compilations

In this second empirical approach, which has also been used for C NMR spectra, predictions are based on tabulated chemical shifts for classes of structures, and corrected with additive contributions from neighboring functional groups or substructures. Several tables have been compiled for different types of protons. Increment rules can be found in nearly any textbook on NMR spectroscopy. 

Useful compilations of NMRspectra are , . The H and NMR chemical shifts and the geminal and vicinal proton-proton coupling constants for oxirane and other heterocycles are given in a very readily compared manner,... 

Dungan, C H, Van Wazer J R Compilation of Reported NMR Chemical Shifts 1951 lo mid-1967 Wiley-Interscience, New York, 1970... 

Englert O published the best and greatest compilation of chemical shifts of carotenoids, including some isomers, which are essential for interpretation of NMR spectra. 

Proton nuclear magnetic resonance (NMR) chemical shifts of 1,2,3-thiadiazoles give another indication of the aromatic character of these compounds. Compiled in Table 4 are a number of examples of proton chemical shifts for ring-substituted 1,2,3-thiadiazoles. 

Typical NMR data were compiled in CHEC-II(1996) <1996CHEC-II(8)2> for 3.77-pyrrolizine 1, its lithium salt, the pyrrolizin-3-one 2, and its regioisomer (pyrrolizin-2-one). More recently, Kissounko et al. <1998JOM(556)145> reported the H chemical shifts of the parent pyrrolizine anion and anion 21a as well as those of their silylated or stannylated derivatives 22-26. 

NMR shifts ( H, 13C, and 1SN) of 1-alkyl-, 2-alkyl-, and 3-aryltetrazolo[l,5- ]pyridinium salts have also been measured <1999JST119>. The data are compiled in Table 3. The 1SN shifts of these salts seemed of particular importance as they revealed quite big shielding changes for the nitrogen nuclei. These chemical shifts were also calculated by the ab initio GIAO-CHF method, and the result was found to be in fairly good agreement with the experimental values. 

Miyamoto and Yamazaki elaborated a general synthetic method to spiro-substituted [l,2,4]triazolo[l,5-c]pyrimi-dines bearing alicyclic rings of different sizes and bearing different (amino and sulfano) substituents in position 5 <1997JHC871>. 13C NMR chemical shifts of the ring carbon atoms of some selected derivatives are compiled in Table 4. 

Beyond routine analytical NMR data, a relatively large set of 13C NMR data is available for derivatives of the [l,2,4]triazolo[2,3- ][l,3,5]triazine 19 ring system <1995J(P1)801, 2002JHC327>. The experimentally observed chemical shifts are compiled in Table 1. 

Systematic NMR studies of a set of heterocycles containing guanidine and thiourea structural moiety have been published by an English team <1995MRC389>. In the frame of these investigations, some imidazo- and thiazolo-[l,2,4]triazinones having the general structure 50 have been analyzed by 13C and 1SN NMR spectroscopy. The chemical shifts of some derivatives are compiled in Table 3. 

The last section is a compilation of useful empirical additivity rules for 13C chemical-shift prediction, regardless of underlying transmission mechanisms. Peculiarities of less common substituents are cited, and, finally, substituent-induced 13C signal shifts in various cyclic compounds are discussed, with special emphasis on their use in conformational analysis I do not, however, claim completeness for this latter discussion. 

Upfield shifts of multiply heterosubstituted carbon atoms are well known in the 13C NMR literature. Some representative examples are shown in Figure 9 and Table 16, where the actual l3C chemical shifts and individual a-SCSs, respectively, for each newly introduced substituent in methane derivatives are compiled. The ICSs can be calculated by subtracting any a-SCS from its respective predecessor within a given row in Table 16. The general trend is toward a distinct decrease of a-SCS with progressive substitution that is, all the ICSs are negative. 

All fluorine chemical-shifts given in this compilation have been converted to the 8 scale, with trichlorofluoromethane (Freon-11) as refer-... 

Duncan, T. M. A Compilation of Chemical Shift Anisotropies, Farragut Press, Farragut, TN. 

Nitrogen NMR data have been obtained using both the low-abundance, spin = 1/2 N and the predominant spin = 1 N nuclei. Several different references have been used for nitrogen NMR including aqueous ammonia, ammonium salts, acetonitrile, nitric acid, and nitrates. Current opinion favors neat nitromethane, and the compilation of the known data for 1,4-oxazines (Table 6) is expressed with respect to this reference and arranged in order of the observed chemical shift. For the C-labeled compound 87, carbamate rotamers lead to two separate signals and the value of 7c n can be determined -283.98 (d, J 9) and -284.46 (d, 7 11) <2001JOC8010>. 

There is sufficient H nuclear magnetic resonance (NMR) data available on the various structural types of 1,3-thiazines to be able to predict the chemical shift of the ring protons <1996CHEC-II(6)383>. A compilation of the data for some new derivatives is displayed in Table 1. 

In many cases it is not easy to identify individual effects or blends unequivocally, because they are not independent from each other in how they influence nuclear shieldings. Compilations of such effects on H and 13C chemical shifts have been presented24,2S, and the following discussion will provide further instances for these and other nuclei. 

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