13C nuclear magnetic resonance spectra. XV—the γ-anti substituent effect and its dependence on substitution at the α- and γ-carbon atom
✍ Scribed by Helmut Duddeck; Md. Rabiul Islam
- Publisher
- John Wiley and Sons
- Year
- 1981
- Tongue
- English
- Weight
- 383 KB
- Volume
- 16
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
It is shown that the y, effects of hetero substituents on the "C chemical shift (7, SCS) are enlarged by +2 to +5 ppm by substituting the a-hydrogen atom by any group or atom (e.g. CH,, OR, F, (3, Br). The same is encountered when the axial y-hydrogen is replaced by CH3, OH or F. If, however, the substituting atom at the y,-carbon atom is a higher-row halogen (Cl or Br), diamagnetic y. SCS for this signal are observed which may even exceed those for nnsubstituted y,-carbon atoms. The removal of a 1,3-diaxial hydrogen-hydrogen interaction and the existence of a still unspecified 'heavy halogen effect'-both diamagnetic contributions to the y, SCS of hetero substituents-are responsible for these 6ndings. Methyl groups do not behave like hetero substituents with respect to the y, SCS.