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Steric effects on carbon-13 NMR shifts: carbon–hydrogen bond polarization contributions

✍ Scribed by Peter Rudolf Seidl; Kátia Zaccur Leal; Valentim Emílio Uberti Costa; Maria Elisabete Stapelbroek Mollmann

Publisher
John Wiley and Sons
Year
1998
Tongue
English
Weight
174 KB
Volume
36
Category
Article
ISSN
0749-1581

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✦ Synopsis

The shielding observed in the chemical shifts of carbon atoms subjected to steric compression was originally attributed to carbonÈhydrogen 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 e †ects. Hydrogen shifts, bond lengths and charge distributions were used as probes for these e †ects in methylnorbornanes and similar tetracyclic norbornyl hydrocarbons. CarbonÈhydrogen bond polarization can make a signiÐcant contribution to shielding and can be distinguished from e †ects caused by changes in dihedral angles due to steric congestion.

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✍ Mahavir Prashad; M. Seth; A. P. Bhaduri; Avijit Banerji 📂 Article 📅 1980 🏛 John Wiley and Sons 🌐 English ⚖ 148 KB 👁 1 views

## Abstract ^13^C NMR of diastereoisomeric pairs of 2,3‐diaryl‐2‐methylbutyronitriles revealed a difference in the chemical shift of the carbon atoms between the diastereoisomers and the observed shifts were greatly influenced by the presence of an __ortho__ substituent in the 3‐phenyl ring.