Chemical shifts rings proton

Table 2 H Chemical Shifts of Protons on the Heterocyclic Rings of Simple Benzazines cf. naphthalene, column 1)...

The -CH2-COOH substituent must therefore reside on the five-membered ring and it defines its position by the chemical shift of the proton that remains on this ring. This substituent has relatively little influence on the chemical shifts of protons ortho to it and so a shift of 7.18 ppm is immediately indicative of a proton in the 2 position and therefore the substituent in the 3... 

In this context, it should be pointed out that the correlation between aromatic solvent-induced shifts (ASIS) and the axial or equatorial orientation of protons in cyclic sulfoxides and sulfites is quite distinct (211-213) and may be utilized in the assignment of configurations. For instance, the absolute configuration at sulfur was assigned to the penicillin sulfoxide 202 based on analysis of the effect of aromatic solvents on the chemical shifts of protons of the thiazolidine ring (214,215). 

The circulating electrons in the 7t-system of aromatic hydrocarbons and heterocycles generate a ring current and this in turn affects the chemical shifts of protons bonded to the periphery of the ring. This shift is usually greater (downfield from TMS) than that expected for the proton resonances of alkenes thus NMR spectroscopy can be used as a test for aromaticity . The chemical shift for the proton resonance of benzene is 7.2 ppm, whereas that of the C-1 proton of cyclohexene is 5.7 ppm, and the resonances of the protons of pyridine and pyrrole exhibit the chemical shifts shown in Box 1.12. 

The proton NMR spectrum of 2,2 -bipyridine has been obtained and analyzed in a variety of solvents by several authors. ° The full interpretation of the spectra is in accord with the transoid conformation I in solution. The behavior of the chemical shifts of protons at positions 3 and 3 indicates the existence of a strong deshielding effect exerted by the nitrogen atoms of the adjacent rings. Interestingly, the proton NMR spectra of 2,2 -bipyridine taken in various solvents indicate self-association and stacking of the molecules in some cases. The spectra of some substituted 2,2 -bipyridines, - - 2,3 -bipyridine, ° 2,4 -bipyridine, ° 3,3 -bipyri-dine, and 4,4 -bipyridine - - ° have been investigated in detail. It was... 

FIG. 8.6 Chemical shifts of protons in benzene, pyridium rings, and methylene groups versus the ratio of moles of solubilized benzene to moles of hexadecyl pyridinium chloride. (Redrawn, with permission, from J. C. Eriksson, Acta Chem. Scand., 17, 1478 (1963).)... 

The values of chemical shifts for protons attached to different functional groups are reasonably constant, so that we can predict the chemical shift of protons in various molecular environments (especially protons attached to an aromatic ring or those of a methylene group) by using some empirical rules (Boxes 4.5 and 4.6). 

Table 4 Chemical Shifts of Protons Bonded to Unsaturated Rings...

Chemical shifts of protons of 1,2-dithiin (Table 4) show no evidence of a ring current, but borderline aromaticity of a 1,2-oxathiin 2,2-dioxide derivative has been inferred from the chemical shift of H-6 which falls midway between that for a proton in a nonaromatic cyclic ether and for H-2 of furan (64JOC1110). 13C shifts of 1,2-oxathiin 2,2-dioxides at the C-4 and C-6 positions have been considered anomalous but may be rationalized by invoking mesomeric withdrawal of electron density from these positions by the SO2 moiety (770MR(10)208>. 

Fulvic acid isolated from Island Lake provided direct spectral evidence of protons attached to aliphatic alicyclic rings. The H NMR spectrum of this sample (Figure 3) has a broad medium-intensity peak near 1.8 ppm. The chemical shifts of protons on aliphatic alicyclic rings are commonly split into two broad peaks centered at 1.1 and 1.8 ppm because of their variable boat and chair configurations (23). 

CHEMICAL SHIFTS OF PROTONS ON MONOSUBSTITUTED BENZENE RINGS... 

TABLE D.5 Chemical Shifts of Protons on Heteroaromatic Rings... 

Table 6 1H NMR chemical shifts of protons on the heterocyclic rings of simple benzazines (cf. naphthalene, column 2)...

Similarly, a series of m- and -substituted anilides 68 of thienoic acid were prepared and their H NMR spectroscopic characteristics were examined. In general, good correlations were observed between the chemical shifts of proton signals of the acyl aromatic rings and the Hammett . 

Table 3.11 Chemical shifts of protons on fused aromatic rings 7.81 8.31 7.91...

The chemical shift of protons bonded to benzene rings, C-C double bonds, and C-C triple bonds merits additional comment. 

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