Unsubstituted ring proton resonances

The temperature dependence of the unsubstituted ring proton resonances are linear functions of T 1 and the slopes of shift vs. T-- - are identical within experimental error to that of uranocene (fig. 7, Table V). The slight difference in intercepts at T-1=0 undoubtedly result from using the proton resonance of cycloocta-tetraene dianion as a diamagnetic reference for all the compounds. 

The IR spectra of the polymer (P) contained two sharp absorptions near 1000 and 1100 cm-- -, indicative of the presence of unsubstituted cyclopentadienyl rings in the products. The 250-MHz - -H-NMR spectrum, shown in Figure 3, contained the expected peaks for the methyl, methylene, and cyclopentadienyl protons, respectively, at 61.52, 1.57 and 4.04 ppm. No olefinic proton resonances were present, and all of the samples of the polymer in Table II exhibited the same - -H-NMR spectrum. 

The protonation of acetyl- and formyl-pyrroles occurs on the carbonyl group (Skylar et al., 1966). So, for example, in the nmr spectrum of 2,4-dimethyl-3-acetyl-pyrrole in concentrated acid the vinyl (C-5) proton resonance is retained, although there is exchange in deuteriated acid (Melent eva et al., 1971). The behaviour of carbethoxy-substituted pyrroles is more complicated, however. While 3-carbethoxy derivatives [168] and the 2-carbethoxy derivatives unsubstituted at the 5-position [169] protonate at the a-position of the ring and are not exceptional, the 2-carbethoxy derivatives with a methyl group at the 5-position [170] give evidence in the nmr... 

PMR studies on 1,3,4-triazaindolizines substituted in 2-, 5-, 6-, or 7-positions show a connection between op and the proton shift relative to the 2- or 6-proton resonance in the unsubstituted compounds.403 The PMR chemical shift in the N-Me group of 5-substituted 2-chloro-l-methylbenzimidazoles correlates with az in CDC13 but with ap in MeCOOH demonstrating the reduction in through resonance on protonating the five-membered ring 404 there is, however, no correspondence of chemical shift produced by 6-substitution with am,404 nor is there any connection between 4-, 5-, 6-, or 7-positional substitution of... 

The importance of these compounds for nmr interpretations is that we can look at the unsubstituted ring in systems where Xx and Xy are not constrained by symmetry to be equal. In both of the monosubstituted uranocenes investigated, the proton resonance of the unsubstituted ring is a singlet. 

At 30°C, the protons of the unsubstituted ring in mono-t-butyluranocene resonate at 0.51 ppm lower field and those in the mono-ester resonate at 0.43 ppm higher field than the ring protons in uranocene. These differences are small but real and were established independently by observing the spectrum of mixtures of these compounds. 

R = CHjPh), which showed a marked shielding effect of the 8a proton by the phenyl ring. In the unsubstituted compound (81, R = H) the triplet due to the 8a proton is found at S 4.93, whereas in both of the dl isomers of the benzyl compound (81, R = CH2Ph) the 8a proton resonates at S 3.07. The explanation of this remarkable shielding effect is the proximity of the aromatic ring of the pseudoaxial 3-benzyl substituent to the 8a... 

Interestingly, they are more basic than the unsubstituted diazine, and always protonate on a ring nitrogen. This allows resonance stabilization of the conjugate acid utilizing the lone pair of the amino substituent. It has been found that one can... 

The resonances of the unsubstituted non-bridge aromatic ring carbon protons are sufficiently separated in the proton NMR spectrum so that the ratio of mono- to di- to triaromatics can be determined,... 

Data relative to the 400 MHz H-NMR spectra of cobalt corrolates are reported in Table 16. The strong shift due to the macrocycle ring current demonstrates that the presence of the meso-phenyl substituents does not cause the loss of aromaticity. The meso-protons of the monophenyl derivative resonate at the same chemical shift value observed for the meso-unsubstituted complex. 

The interplanar distance in unsubstituted HBC is 0.342 nm,164 and thus the aromatic protons of one layer will experience the ring currents of the extended -electron systems of adjacent layers. In HBC—C12, three different aromatic proton environments can thus be identified with respect to the degree to which the proton experiences the ring current of the adjacent layers. The unshaded circles represent protons that lie neither above nor below the 71 orbitals of an adjacent layer, and therefore correspond to the least shielded resonance (highest ppm). Fully shaded and hatched circles then represent protons that lie over or below an inner and outer part, respectively, of an adjacent ring system the fully shaded protons would be expected to be the most shielded. Assigning the unshaded, hatched, and fully shaded protons to the A, B, and C resonances in Figure 23b, respectively, the observed presence of... 

Dithienylalkanes that are unsubstituted elsewhere in the thiophene rings show the typical ABX pattern the proton at C-5 resonates at the lowest field. 

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