ISSN:
0030-4921
Schlagwort(e):
Chemistry
;
Analytical Chemistry and Spectroscopy
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
17O chemical shifts of axial hydroxyl groups in cyclohexanols are upfield of those of corresponding equatorial groups, but in 5-hydroxy-1,3-dioxanes the opposite is observed: the axial OH resonates downfield of the equatorial OH. The situation is the same in the corresponding methyl ethers and is, thus, not a result of intramolecular hydrogen bonding in the axial 5-hydroxy-1,3-dioxane, but appears to parallel the effect on 13C and 19F shifts observed in corresponding equatorial and axial 5-methyl- and 5-fluoro-1,3-dioxanes, which has been attributed to an upfield shifting effect of the antiperiplanar γ-located heteroatoms. Surprisingly, the reciprocal effect is not seen in the ring 17O shifts of the 5-hydroxy-1,3-dioxanes. A δ compression shift is seen in the 17O spectrum of trans-3,3,5-trimethylcyclohexanol (syn-axial OH and CH3), analogous to the effect earlier reported in 13C spectra. Conversion of four of the alcohols to methyl ethers produces a large upfield effect on the 17O shift, larger in the cyclohexanols than in the 1,3-dioxane-5-ols. Similar upfield shifts have been recorded in the literature; their extent depends on whether the alcohols are primary, secondary or tertiary.
Zusätzliches Material:
2 Tab.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/omr.1270210307
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