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Theoretical and empirical calculations of the carbon chemical shift in terms of the electronic distribution in molecules
Author(s) -
Martin G. J.,
Martin M. L.,
Odiot S.
Publication year - 1975
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.1270070103
Subject(s) - electronegativity , chemistry , steric effects , valence electron , carbon atom , valence (chemistry) , electronic structure , computational chemistry , atomic physics , molecule , electronic effect , electron , physics , quantum mechanics , stereochemistry , organic chemistry , alkyl
The principles of the theoretical calculations of the carbon atom screening constant are reviewed. The Independent Electron, SCFMO and Valence Bond formulae are briefly discussed, and the relative importance of the different terms involved in an approximate decomposition of σ 13 C are pointed out. The variations of the excitation energy Δ E , the mean distance between the nucleus and 2p electrons, and the electronic charges and bond orders with the structure are presented. The nature of the steric effect is also explained. In a second part the various empirical correlations which make an evaluation of δ 13 C from structural and physical properties possible are shown. The actual substituent parameters of the main classes of compounds are listed and worked examples given to make the use of the tables easier. The correlations between δ 13 C and the electronic charge, electronegativity, Hammett‐Taft constants, electric field effects, geometrical parameters, spectroscopic data (electronic transitions, screening of other nuclei) and pH are also discussed with a view to appraising the carbon screening.