Kinetic Solvent Effects on Hydrogen-Atom Abstractions: Reliable, Quantitative Predictions via a Single Empirical Equation<sup>1</sup>
Bibliographic record
Abstract
The rate of hydrogen-atom abstraction from XH by a radical, Y •, can be solvent-dependent. In many cases, the kinetic solvent effect (KSE) is directly related to hydrogen-bonding interactions between XH and the solvent. The relative hydrogen-bond acceptor (HBA) properties of solvents are given by constants of Abraham et al. (Abraham, M. H.; Grellier, P. L.; Prior, D. V.; Morris, J. J.; Taylor, P. J. J. Chem. Soc. Perkin Trans. 2 1990, 521−529). Room-temperature rate constants for hydrogen-atom abstraction,, have been determined in a number of solvents, S, where XH refers to several substituted phenols, tert -butyl hydroperoxide or aniline and Y • is a tert -alkoxyl radical. In all cases, plots of log( /M - 1 s - 1 ) versus gave excellent linear correlations, the slopes of which, M XH, were found to be proportional to the hydrogen-bond-donating (HBD) ability of XH, as scaled with parameters of Abraham et al. (Abraham, M. H.; Grellier, P. L.; Prior, D. V.; Duce, P. P.; Morris, J. J.; Taylor, P. J. J. Chem. Soc., Perkin Trans. 2 1989, 699−711), with M XH = − 8.3 . This leads to a general empirical equation which quantifies KSEs at room temperature: log = log − 8.3, where refers to the rate constant in a non-HBA solvent for which = 0, generally a saturated hydrocarbon. Since M XH depends only on XH, rate constants for hydrogen-atom abstraction from XH by any Y • can be accurately predicted in any of the several hundred solvents for which is known on the basis of one single measured rate constant, provided for XH is known or measured. HBA solvents can have profound effects on some of the reactions and thermodynamic properties of hydroxylic substrates including: (i) reaction product profiles (ii) antioxidant activities, (iii) Hammett-type correlations, and (iv) O−H bond dissociation enthalpies. Finally, literature data (Nielsen, M. F.; Hammerich, O. Acta Chem. Scand, 1992, 46, 883−896) on KSEs for two proton-transfer reactions are shown to be correlated by the same equation which correlates KSEs for hydrogen-atom transfers.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 | 0.009 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.003 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.003 |
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".