| Autor: |
Seidl, Peter Rudolf, Leal, Kátia Zaccur, Costa, Valentim Emílio Uberti, Mollmann, Maria Elisabete Stapelbroek |
| Zdroj: |
Magnetic Resonance in Chemistry; April 1998, Vol. 36 Issue: 4 p261-266, 6p |
| Abstrakt: |
The shielding observed in the chemical shifts of carbon atoms subjected to steric compression was originally attributed to carbonhydrogen bond polarization. There is increasing evidence that this is not universally the case and theoretical studies reveal that changes in dihedral angles may be responsible for many steric effects. Hydrogen shifts, bond lengths and charge distributions were used as probes for these effects in methylnorbornanes and similar tetracyclic norbornyl hydrocarbons. Carbonhydrogen bond polarization can make a significant contribution to shielding and can be distinguished from effects caused by changes in dihedral angles due to steric congestion. © 1998 John Wiley & Sons, Ltd. |
| Databáze: |
Supplemental Index |
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