13C NMR spectra of polyalkoxymethanes, and their sulphur- and nitrogen-containing analogues, of an aliphatic series. Inclusion of non-bonded interactions by the use of CO bond increments
✍ Scribed by V. I. Dostovalova; S. S. Zlotsky; D. L. Rakhmankulov; A. B. Terent'ev
- Publisher
- John Wiley and Sons
- Year
- 1987
- Tongue
- English
- Weight
- 526 KB
- Volume
- 25
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
C NMR spectra of 40 substituted acetals, carbonates, ortho ethers, 1,3-dioxocycloalkanes, 1,3-oxothiolanes and 1,3-0xazolidines were studied. The chemical shift of the C-a carbon atom was found to depend both on the number ( K ) and type of the hetero substituents at C-a. The effect of oxygen, nitrogen and sulphur atoms on the C-a chemical shift was shown to be a non-additive property relative to the unsubstituted isostructural hydrocarbons. The C-a chemical shift in the linear and cyclic polyalkoxymethanes can be described by an equation incorporating C -0 bond increments and contributions from the RO substituents:
6(I3C-a) = 6('3CH,)+KA6(C-O)+~, ARO
The C -0 increment depends quadratically on the number ( K -1) of geminal neighbours of the oxygen atom under study. Good agreement between the experimental and calculated shifts can only be achieved by inclusion of nonbonded interactions between the geminal heteroatoms.