Chemical shift of protons

Neural networks can learn automatically from a data set of examples. In the case of NMR chemical shiffs, neural networks have been trained to predict the chemical shift of protons on submission of a chemical structure. Two main issues play decisive roles how a proton is represented, and which examples are in the data set. 

TABLE 1-33 CHEMICAL SHIFTS OF PROTONS OF THE SUBSTITUENTS IN SUBSTITUTED THIAZOLE (235)... 

Table 7.44 Estimation of Chemical Shift of Proton Attached to a Double Bond 7.95...

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

Fig. 3-4. (A) Changes in chemical shift of protons of cyclophane -CH - groups between bipyridinium and phenyl in H NMR spectra of 3 as a function of (R)-DOPA concentration (a) 0, (b) 0.111, and (c) 0.272 mol (B) Change in chemical shift plotted against the analytical concentration of (R)- and (5)-DOPA. The solid line is calculated for 1 1 host - guest complexation. (Reprinted with permission from ref. [79]. Copyright 1998, American Chemical Society.)...

Fig. 12-1. Correlation between azo coupling rates of substituted benzenediazonium ions with the 2-naph-thoxide-3,6-disulfonate trianion and the chemical shifts of protons at the position of the diazonio group in NMR spectra of the corresponding monosubstituted benzene parent compounds (Diener and Zollinger, 1986).

Fig. 1. Changes in the chemical shift of protons lining the cleft of 13 (H4) H,) as P-phenyl-ethylamine is added...

Approximate chemical shift of proton (ppm) = 5.25 + Zgem + Zcis + Ztrans... 

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... 

Chemical shifts of protons in hydrogen-bonded complexes... 

NMR chemical shifts of protonated carbonic acid 109 and 110 were investigated experimentally and computationally using IGLO/II chemical shift calculations for MP2/6-31G(d) optimized geometries.140... 

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). 

Chemical shifts of proton addition complexes of some methylbenzenes (according to Brouwer el al., 1965a)... 

The chemical shift 5, defined by Equation (22), was measured at 40.0 and 15.6 Mc./sec. and was found to be —3 2 relative to water for both SA and SG. The derivatives of the resonance absorptions were recorded in the measurements. If the total anisotropy of the chemical shift of protons in the solid is somewhat less than the line width, the cross-over point of the derivative will correspond to the average value of S as for liquids, and will be directly comparable with the shifts for protons in the liquid state. Comparison of the shift value with those of H3O+ (aqueous) (1 1), S = -1-11, OH (aqueous) (121), S = -1-10 dilute solutions of alcoholic-type protons... 

AC2O/S11CI4), and nitration [Cu(N03)2] of thienothiophenes 1 and 2. He recently also studied the effect of the a-substitution (with halogen, CH3, SCHj, CN, NO2, COCH3, and COOH groups) on the chemical shifts of protons. He observed a good correlation between the shifts, reactivity constants, F (the field effect), and R (the resonance effect). ... 

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). 

The absolute chemical shifts of protons in diamagnetic solids are typically near 30 ppm (28), and the Knight shift caused by conduction electrons through contact interaction is estimated to be —31.2 ppm, using the experimental T1T value of 180 JK-sec and the Korringa relation (29) ... 

The chemical shifts of protons in a given type of chemical group vary... 

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>. 

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