Bibliographic record
Abstract
Abstract 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, pKa′, 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 pKa′ but significant deviations from the correlation increase in the order CH2Ph (0.19) p‐O‐i‐Pr (1.38) p‐YC6H4 groups increase linearly with decreasing pKa′ as Y changes in the order Me2N (0.29) 3C (0.60). The new substituent effects for these ‘deviant’ groups that can be derived from the linear correlations of σ* with pKa′ are different (even in sign for the p‐Me2NC6H4 group) from the original values of the Taft parameter, and they are much smaller than the additional effects detected here. These results show that σ* values contain within themselves a variety of new features that should be compared with those shown by parameters used in more recent QSAR analyses, and that might be useful in such analyses. Copyright © 2004 John Wiley & Sons, Ltd.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.013 | 0.026 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.002 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.003 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".