Axial protons chemical shifts

It is clear from the above work on B12 and the inorganic models that changing the axial Ugands has a noticeable effect on the corrin system, as evidenced by the C(10)-proton chemical shift. On the other hand,... 

It is concluded that one isomer has the methyl group below the basal plane of the boron framework (endo-) with the CF3 group nearly in the plane of the base in an axial (exo-) position and in the other isomer the conformation is the opposite, but no assignment was made. Marynick and Onak 180> have suggested, on the basis of their ring current model for the correlation of chemical shifts in pyramidal boron compounds, that the proton chemical shifts reported for the methyl groups of these two isomers 174> favor assignment of the endo-methyl conformation to isomer A. 

Ikeue et have characterized temperature-dependent spin crossover processes in a series of saddle-shaped (S4) ferric porphyrins, using for this purpose proton chemical shifts of the axial ligand resonances. Curie plots showed dra-... 

In cis-l,3-di-t-butylcyclohexane changes in the chemical shifts of ring protons indicate an almost additive effect of t-butyl groups. The 2-axial proton is shifted 0.56 p.p.m. upfield and the 2- and 4-equatorial protons downfield 0.15 and 0.05 p.p.m., respectively. The coupling constant J... 

One property of NMR spectroscopy is that it is too slow a technique to see the mdi vidual conformations of cyclohexane What NMR sees is the average environment of the protons Because chair-chair mterconversion m cyclohexane converts each axial pro ton to an equatorial one and vice versa the average environments of all the protons are the same A single peak is observed that has a chemical shift midway between the true chemical shifts of the axial and the equatorial protons... 

According to van deer Veen (27) and Rao and Foster (17 the anomeric proton line positions for a-D-glycopyranosides (H equatorial) appear in the region of 4.8 to 5.5 p.p.m., while for / -D-glycopyranosides (Hi axial), the peaks appear at 4.4 to 4.6 p.p.m. The chemical shift of the anomeric proton of methylkasugaminide (5) is located at 4.57 p.p.m. and thus the proton must be axial, excluding structure 8b and 8c in which the anomeric proton is equatorial. Structure 8a is thus completely in agreement with the NMR spectra. 

The power of the new spectrometer to reveal configurations of difficult cyclitols or sugars was first tested with mt/o-inositol (2), using deuterium oxide as solvent. At 60 or 100 MHz. the one equatorial and five axial protons appear to have different chemical shifts as shown by Lemieux in 1956 with a 40 MHz. instrument (14,15). However, since the five-proton axial signal could not be resolved, one could probably not have assigned the configuration 2 (which was already known from laborious chemical correlations extending over many years.)... 

Table IV. Comparison of Anomeric Proton (Hi) Chemical Shifts for Free and Acetylated D-gluco and D-mannopyranoses With Those of Related 2-Deoxy Sugar Derivatives. Effect of Replacing an Axial or an Equatorial C2-Methylene Proton With a Hydroxy or Actetoxy Substituent...

The proton spectra analysis of thietane, thietane oxide and thietane dioxide at 100 and 300 MHz in the temperature range — 140 to 190 °C confirmed the puckered structure for the oxide (5a) with the sulfinyl oxygen in the equatorial orientation, as inferred from chemical-shift considerations180. It appears that the repulsive-type 1,3-interactions between the oxygen and the 3-substituents184 are operating between oxygen and the axial proton on C-3 in the unsubstituted thietane oxide (5a). For the thietane dioxide (5b ... 

The H NMR spectra of the epimeric cyclohexanols in DMSO reveal that the hydroxyl proton in the axial alcohol shows a resonance absorption at a higher field than in the equatorial one, indicating that the conformational effect of the hydrogen bond influences the NMR chemical shifts . 

Proton c can be defined by the fact that it is not equatorial and it is highly coupled. The multiplet at 3.82 ppm satisfies these requirements. It is in the right ball park for chemical shift and is highly complex in that this proton is already the X part of an ABX system coupled to both protons alpha to the chlorine (the AB part). It is then further coupled with a 10 Hz, axial-axial coupling (reciprocated in the dd at 2.07 ppm) and with a 2 Hz axial-equatorial coupling which is reciprocated in the ddd at 2.90 ppm. Note that c and d are not fully resolved from each other. Such overlap inevitably complicates the issue. 

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