Predicted proton resonance

A different type of dynamic process involving a polynuclear metal system has been identified in [(CH C H,)ltRul)Sl(]2+, which has a distorted cubane-like structure with three Ru—Ru bonds in the crystalline state (Fig. 15.56). By following its methyl and ring proton resonances over a temperature range from +70 to —43 BC (Fig. 1537), the complex is shown to undergo a dynamic process involving the metal-metal bonds. At the low-temperature limit, the spectrum contains features predicted for the static structure two lines of equal intensity for the methyl protons... 

For benzene, [6]annulene, with six it electrons (4n + 2, n = 1), the theory clearly meets both tests. As we have pointed out, there is a substantial stabilization of about 37 kcal mole-1 compared with a hypothetical localized model. The familiar chemical properties also point to a strong tendency for maintenance of the six it electron unsaturated system. The proton magnetic resonance spectrum of benzene and its derivatives shows the proton resonances in the range of 8 = +7 to +8 ppm (downfield from tetramethylsilane), 1-2 ppm lower than protons attached to nonbenzenoid double bonds. Referring to Figure 1.21a, we can see that the prediction is in agreement with this result. The induced field adds... 

Figure 2. Predicted spectrum for the hydroxylic proton resonance of [(CH8)3PtOH h observed spectrum redrawn from Ref. 41...

The predicted 1 2 3 2 1 quintet is precisely what we observe for the residual proton resonance in deuterated solvents such as acetone-dg, DMSO-dg or methanol-d. ... 

A full assignment of the proton resonance of substituted 2-styryl-5-nitroimidazoles was carried out by the use of an addition increment method for chemical shift prediction [353]. Some 4-styryl-5-nitroimidazoles have been studied in [354],... 

Mathematical procedures for calculating structural features of cyclocopolymers and of copolymers derived from them are proposed and are used in studies on the 1H-NMR spectra of styrene-methyl methacrylate copolymers derived from styrene-(methacrylic anhydride) copolymers. Reactivity ratios and cycliza-tion constants for styrene-methacrylic anhydride copolymerization were determined from structural features of the derived styrene-methyl methacrylate copolymers. The amount of uncyclized methacrylic anhydride units present in styrene-methacrylic anhydride copolymers having high styrene contents is considerably less than that predicted by these copolymerization parameters. The methoxy proton resonances of the derived copolymers are more intense in the highest field methoxy proton resonance area than would be expected if such resonance were due only to cosyndiotactic SMS triads. Possible explanations for these discrepancies are proposed. 

Hexadehydro-[ 18]annulene 80>, 15, (see Table 4) possesses no inner protons and the six equivalent outer protons resonate at t 2.98. This represents a downfield shift of over 1 ppm from a model compound, cis-hex-3-ene-l,5-diyne, 9, (t 4.11). This model compound also served to clarify the interpretation of the singlet at t 5.55 in the case of l,5,9-tridehydro-[12]annulene, 1, a molecule for which aromaticity is not predicted. The downfield shift of 15 and the upfield shift of 1 from the acyclic model can then be attributed to a diamagnetic ring current in 15 and a paramagnetic ring current in 1. 

Finally, the peak for the protons on the methylene group adjacent to the earbonyl should appear as a sextet downfield from the other methylene proton resonances. The group at 6 - 2.4 is consistent with our prediction. 

A reasonable linear relation has been observed between 6 and the NMR proton resonance in a series of compounds of the carbonyl type (3). Although this cannot be directly predicted from the above considerations we intuitively expect such a relation to be obtained for compounds of similar type and stereochemistry. 

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