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The NMR spectra of the carbanions of xanthene and thioxanthene. Evidence for paratropism
Author(s) -
Vos H. W.,
Bakker Y. W.,
MacLean C.,
Velthorst N. H.
Publication year - 1974
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270060413
Subject(s) - carbanion , xanthene , chemistry , chemical shift , ring (chemistry) , spectral line , methyl iodide , nmr spectra database , nuclear magnetic resonance , computational chemistry , stereochemistry , photochemistry , medicinal chemistry , organic chemistry , physics , astronomy
The proton NMR spectra of the carbanions of xanthene [XH] − and thioxanthene [TxH] − have been recorded and interpreted. Paratropism in the central rings of [XH] − and [TxH] − is inferred from a comparison of the chemical shifts with those of the carbanion of 9,10‐dihydroanthracene [AH] − . The contributions to the chemical shifts arising from n‐electron excess charges, local dipoles and magnetic anisotropies are discussed. Numerical values for the various ring currents have been estimated by a least squares analysis of the observed chemical shifts after applying corrections for the excess charge effect. The results point to a strongly increasing paramagnetic ring current in the central ring in the order [AH] − , [TxH] − , [XH] − .
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