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Deconstruction of Taft's σ* parameter: QSAR meets QALE
Author(s) -
Babij Claudia,
Poë Anthony J.
Publication year - 2004
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.708
Subject(s) - chemistry , substituent , taft equation , linear correlation , quantitative structure–activity relationship , alkyl , ligand (biochemistry) , linear relationship , stereochemistry , medicinal chemistry , computational chemistry , organic chemistry , receptor , mathematics , statistics , biochemistry
Taft's σ* parameter has been mostly disregarded in QSAR (quantitative structure–activity relationships) analyses because it appears to reveal only simple field‐inductive substituent effects. However, it can be shown that, when a reference reaction different from that adopted by Taft is used, the σ* values reveal considerably more subtle features. This occurs when a reference reaction parameter, p K a ′ , is used that is closely related to the Brønsted basicity of P‐donor molecules and that is regarded in QALE (quantitative analyses of ligand effects) analyses as measuring the purely σ‐donor properties of the phosphines. Values of Taft's σ* parameter for alkyl groups show an excellent linear correlation with p K a ′ but significant deviations from the correlation increase in the order CH 2 Ph (0.19)