13C chemical shifts of symmetrically substituted biphenyls: Unambiguous signal assignment for the carbons ortho and para to an aryl group
- 1 December 1981
- journal article
- research article
- Published by Wiley in Magnetic Resonance in Chemistry
- Vol. 17 (4) , 250-256
- https://doi.org/10.1002/mrc.1270170406
Abstract
The natural abundance 13C NMR spectra of 2,2′‐dimethyl‐, 2,2′‐dimethoxy‐ and 2,2′‐dihydroxybiphenyls, and a series of 2,2′‐dimethoxy‐5,5′‐disubstituted biphenyls were recorded. Unambiguous signal assignments of the carbons ortho and para to an aryl ring in biphenyls were made by selective deuteration and/or the graphical method for 1H single frequency off‐resonance decoupled spectra. Contrary to the reported assignments, it was shown that the signal for C‐6 in 2,2′‐dimethylbiphenyl clearly appears at lower field than that for C‐4. The signals for the ortho carbons (C‐6) of 2,2′‐dimethoxy‐5,5′‐disubstituted biphenyls generally appeared at lower fields than those for the para carbons (C‐4). The validity of applying deuterium isotope shifts to the assignments of 13C chemical shifts of di‐ and tetra‐substituted biphenyls is also discussed.Keywords
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