Chemical shifts table

Frequently the chemical shifts (Table 2.3) of molecular fragments and functional groups containing nitrogen complement their H and C shifts. The ammonia scale of N shifts used in... 

A systematic NMR spectroscopic study of these adducts suggests that the steric repulsion between the trimethyl aluminum Lewis acid and the phosphane Lewis base rather than the electronic factors account for the detected changes in the P-NMR spectroscopic chemical shifts (Table 1). The change in the chemical shift (A) of the phosphanes on coordination to AlMe3 has been correlated to the... 

Structure 6.8 demonstrates a most extreme example of anisotropy. In this unusual metacyclophane, the predicted chemical shift (Table 5.8) of the methine proton that is suspended above the aromatic ring would be 1.9 ppm. In fact, the observed shift is -4 ppm, i.e., 4 ppm above TMS The discrepancy between these values is all down to the anisotropic effect of the benzene ring and the fact that the proton in question is held very close to the delocalised p electrons of the pi cloud. 

The nB NMR chemical shifts (Table 3.13) demonstrate that the boron atom in all known nitronates is tetracoordinated, that is, it is additionally coordinated by... 

PMR spectrometry is an extremely useful technique for the identification and structural analysis of organic compounds in solution, especially when used in conjunction with infrared, ultraviolet, visible and mass spectrometry. Interpretation of PMR spectra is accomplished by comparison with reference spectra and reference to chemical shift tables. In contrast to infrared spectra, it is usually possible to identify all the peaks in a PMR spectrum, although the complete identification of an unknown compound is often not possible without other data. Some examples of PMR spectra are discussed below. 

It has previously been concluded that even in strong acidic solution, the dioxotetracyanoosmate(VI) complex cannot be protonated to form the oxo aqua complex or even the corresponding hydroxo oxo complex. The pA i and pKa2 values have been estimated to be substantially less than -1, which is also supported by the relationship between pKa values and 170 and 13C chemical shifts (Table II). Extreme slow kinetic behavior, as expected in the case of a +6 charged metal center for a dissociative activation exchange process, has been observed, with only an upper limit for the oxygen exchange determined (Table II). 

The routine use of NMR techniques in the analysis of 1,2,4-trioxolanes and related rings has increased considerably in the last two decades. A general summary of proton chemical shifts reported for various substituted and unsubstituted compounds is given in Table 4. A similar summary of carbon chemical shifts (Table 5) illustrates their use in the analysis of substituted trioxolanes. 

Nuclear magnetic resonance (NMR) spectra of 1,2,3-selenadiazoles have been described previously <1996CHEC-11(4)743, 1981ZNB1017>. The characteristic 111 chemical shifts of H-4 and H-5 lie in the range S 8.2-8.4 and S 8.8-9.4ppm, respectively. The newly reported data also show similar chemical shifts (Table 19). 1J H-Se for 4-substituted-l,2,3-selenadiazoles and V and 2J C-Se coupling constants for 4,5-disubstituted-l,2,3-selenadiazoles were also reported (Tables 19 and 20). 

Takao and co-workers (60) have examined a number of hydro-benzo[c]phenanthridine alkaloids and their derivatives by a variety of physical methods in order to determine the conformation of the B/C rings (Fig. 18). The 13C chemical shifts (Table XVII) were particularly sensitive to the influence of substituents on the conformation of the B and C rings. Chelidonine (94) for example, with a cis ring junction, has both the B and C rings as half-chairs [see Fig. 1 in (60)]. Acetylation of the hydroxy l group to form 95 shielded C-6, C-12, and C-13 relative to 94. The interpretation of these observations was that ring C in 94 adopted a twist half-chair conformation which increased the number of gauche interactions for these carbons. 

The 119Sn NMR chemical shifts (Table 7) seem not to be correlated to the negative charge on the metal. Moreover, the 207Pb resonance of Pl Pb- appeared at an extremely low field shift (+1040 to +1060 ppm)116 (Table 7). 

Note the similarity of this diagram to that for proton chemical shifts on page 553, with the difference that the carbon chemical shifts are about 20 times larger than the hydrogen chemical shifts. Table 14.2 provides a somewhat more detailed summary of carbon chemical shifts. 

Since the chemical shift of a proton is determined by its environment, we can construct a table of approximate chemical shifts for many types of compounds. Let s begin with a short table of representative chemical shifts (Table 13-3) and consider the reasons for some of the more interesting and unusual values. A comprehensive table of chemical shifts appears in Appendix 1. 

The unexpected downfield shift in 66a,b, in connection with strong temperature and solvent effects on the 29Si chemical shift (Table XXI), indicates that the dibromo complexes 66, unlike the difluoro- (64) and dichloro- (65) analogs, undergo ionization to form the bromide salts (68) already at room temperature (Eq. 27).20,52... 

The salts 82-85 were characterized by their typical pentacoordinate 29Si chemical shifts (Table XXV), by the equivalence of the two chelate rings resulting from the molecular C2 symmetry, and by spectral analogy with a binuclear disiliconium dichloride salt (86) for which a crystal structure (Fig. 46) was obtained. 

For several of the siliconium salts crystal structure analyses were obtained, confirming the pentacoordination and the ionic nature of the compounds (well separated cations and anions). The crystal structures for 90a(OTf), 90c(OTf), 91a(OTf), 91a(AlCl4), and 93a(OTf) are depicted in Figs. 47-51, respectively. Further structural support is found in the 29Si NMR chemical shifts (Table XXVI). A remarkable observation in Table XXVI is the nearly equal 29Si chemical shifts of siliconium salts sharing the same silicon complex, but with different anions [e.g. 91a(OTf), 91a(Br), and 91a(AlCl4)] the equal shifts are the evidence that the siliconium cations are essentially independent of... 

The binuclear siliconium salts 57 have two chiral centers at the silicons and hence exist as dj and meso diastereomers. Only the latter isomers were isolated and characterized by crystallographic analysis mes6>-57a(OTf) and meso-51c(OTf) (Figs. 52 and 53). The characterization is further confirmed by the 29Si chemical shifts (Table XXVI) which are in agreement with those for similar mononuclear siliconium salts. 

The structural evidence for 97, 98 came from their characteristic 29Si chemical shifts (Table XXVIII), and a crystal structure analysis for 97a(OTf), the triflate salt derived from anion exchange with 97a (Fig. 56, Table XXIX). Table XXVIII shows that these two salts, the chloride and triflate, have the same 29Si chemical shifts, thus confirming the identical siliconium cation parts in both. In fact, from Table XXVIII it is also evident that the NMR spectra for the two siliconium... 

---