NMR downfield shift

The dimensionless acceptor number, AN, ranked the acidity of a solvent and was defined for an acidic solvent A as the relative P NMR downfield shift (A3) induced in triethyl phosphine when dissolved in pure A. A value of 0 was assigned to the shift produced by the neutral solvent hexane, and a value of 100 to the shift produced by SbClj. Gutmann suggested that the enthalpy of acid-base adduct formation be written as ... 

C NMR. The membrane perturbation by PRC H+ is found to be relatively smaller than DBC H. The ring current effect on the EPC h NMR signal is not substantial at any site. Only significant NMR downfield shift is noticed in the carbonyl site, as shown in Fig. 10. The difference in the perturbation effect between DBC H and PRC H supports the difference in the trapped site in bilayers and that in the anesthetic mechanism between the two drugs. 

In contrast to 2, the above derivatives incorporate four hydrogen bond donors. As a consequence, a favourable bonding situation is present in which the four secondary amine protons of each host can interact with the two charged carboxylate groups of the guest - see 4a and 4b. The proposed structure of the complex of the bis-urea derivative was supported by the existence of large NMR downfield shifts for both the inner and outer urea NH resonances in deutero-dimethyl sulfoxide and the observation of intramolecular H NOEs between the receptor aryl and the guest CH2 resonances in this solvent. A Job s plot confirmed the 1 1 stoichiometry of the product. 

As shown in Scheme 16, treatment of iridacyclohexadienone C with PMea, followed by protonation with triflic acid, generates iridaphenol 17. Again, comparison of the H NMR spectrum of 17 with that of precursor E shows significant downfield shifting of ring protons HI and H3, consistent with aroma-tization of the ring. In the C NMR, downfield shifts of 20-30 ppm are observed for ring carbons Cl, C3, and C5 (Table 2). 

Used in conjunction with Ag(fod)3 as nmr downfield shift reagent for aromatic protons. Commercially available. Hygroscopic white cryst. Insol. H2O sol. CHCI3. Mp 125-132°. Volatile in vacuo. Forms adducts with Lewis bases. 

In solution the cis and trans isomers may co-exist, as demonstrated by N NMR and UV-visible spectra. The N NMR chemical shift of the trans isomer is shifted ca. 60 ppm downfield relative to the cis isomer." The visible absorption band of S-nitrosothiols corresponds to a weak n K transition in the 520-590 nm region. The absorption maxima of trans conformers are red-shifted by ca. 30 nm relative to those of the cis isomer. Two absorptions are observed in the 520-590 nm region in the experimental spectra of RSNO derivatives." ... 

The intramolecular Se N interactions in complexes of the type 15.5 result in a downfield shift in the Se NMR resonances the magnitude of this shift corresponds approximately to the strength of the interaction. ... 

Hydrogens on carbon next to an ether oxygen are shifted downfield from the normal alkane resonance and show U-f NMR absorptions in the region 3.4 to 4.5 8. This downfield shift is clearly seen in the spectrum of dipropyl ether shown in Figure 18.4. 

Ether carbon atoms also exhibit a downfield shift in the 13C NMR spectrum, where they usually absorb in the 50 to 80 5 range. For example, the carbon atoms next to oxygen in methyl propyl ether absorb at 58.5 and 74.8 8. Similarly, the methyl carbon in anisole absorbs at 54.8 8. 

Ring current (Section 15.8) The circulation of tt electrons induced in aromatic rings by an external magnetic field. This effect accounts for the downfield shift of aromatic ring protons in the lH NMR spectrum. 

Proton noise decoupled 13C-NMR spectra of equimolar mixtures of the cyclic hexamer and metal thiocyanates showed that the signals of the carbonyl carbon and two methine carbons gave downfield shifts upon the addition of metal thiocyanates, while those of the three methylene carbons of the tetrahydropyran ring gave upfield... 

Possibly the most characteristic piece of information one can obtain to prove the existence of a I-heteroaallene is the central carbon C NMR chemical shift. This carbon chemical shift is very deshielded. typically being greater than 200 ppm, which stands out from most other carbon resonances in a normal organic molecule. Most of the group 14 I-heteroallenes listed in Table VII have shifts greater than 200 ppm. Also, as the heteroatom becomes larger, the resonance moves farther downfield. 

H NMR spectroscopy studies of iron(IIl) a-alkyl and o-aryl porphyrins have been very important in elucidating spin states. Alkyl and most aryl complexes with simple porphyrin ligands (OEP, TPP, or TTP) are low spin, S — I /2 species. NMR spectra for the tetraarylporphyrin derivatives show upheld resonances for the porphyrin pyrrole protons (ca. — 18 to —35 ppm), and alternating upfield and downfield hyperfine shifts for the axial alkyl or aryl resonances. For -alkyl complexes, the a-protons show dramatic downfield shifts (to ca. 600 ppm), upfield shifts for the /3-protons (—25 to — 160 ppm) and downfield shifts for the y-protons (12 ppm). The cr-protons of alkyliron porphyrins are not usually detected as a result of their large downfield shift and broad resonance. These protons were first detected by deuterium NMR in the dcuterated complexes Fe(TPP)CD3 (532 ppm) and Fe(TPP)CD2CDi (562, -117 ppm). ... 

Fig. 21. XH NMR spectrum of (top) 8 and (bottom) 15, highlighting the downfield shift for resonances of the methylene group attached to N9. Reproduced with permission from Ref. (56). Copyright 2001, Wiley-VCH.

The 3IP NMR chemical shifts, shown in Table IV, should be a useful indicator of the electronic environment at phosphorus. Almost all the 3IP chemical shifts are upfield (negative 8 values) in contrast to the boron-phosphorus compounds where downfield shifts (positive 8 values) are observed. This can be interpreted in terms of weak gallium-phosphorus it-... 

In the l3C-NMR spectrum of the iminosilane, the C20 signal of the THF molecule appears at 73.78 ppm—a downfield shift of nearly 6 ppm compared with that for free THF. This reflects the strong Lewis acid character of three-coordinated silicon in the iminosilane. 

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