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A CNDO/2 study on the additivity and the nature of the non-additivity of the substituent effects on 13C NMR shifts in chlorobenzenes and chlorophenols

✍ Scribed by Reino Laatikainen

Publisher
John Wiley and Sons
Year
1980
Tongue
English
Weight
474 KB
Volume
14
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

The general correlation between the electron densities and the ^13^C NMR chemical shifts is found to be quite poor in the cases discussed. The non‐additivities of the substituent effects on the chemical shifts and the CNDO/2 electron densities correlate only weakly. However, when the electron densities are made specific to different types of atomic orbitals, the s electrons have a pronounced effect in all the models tested. This is explained by an indirect effect on the 〈1/r^3^〉 term of the p electrons. Good correlations are found between the sums of the chemical shifts and the corresponding sums of the substituent charge excesses. The different behaviour of OH and Cl substituents in the additivity of the substituent effects can be explained by their different back‐bonding properties.

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