Medium effects on the α-effect in DMSO–H<sub>2</sub>O mixtures — Comparative studies of <i>p</i>-nitrophenyl benzoate and acetate — Dissection of ground-state and transition-state effects
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Bibliographic record
Abstract
In a study of the origin of the α-effect and its dependence on the nature of the reaction medium as well as structural effects, we report herein a kinetic study of the reactions of p-nitrophenyl benzoate (PNPB) with butan-2,3-dione monoximate (Ox – , α-nucleophile) and p-chlorophenoxide (p-ClPhO – , the reference nucleophile) in dimethyl sulfoxide (DMSO)–H 2 O mixtures of varying compositions at 25.0 ± 0.1 °C. The second-order rate constants (k N ) decrease modestly on addition of DMSO to the medium up to 10 mol% DMSO but increase significantly beyond that point for both nucleophiles. Ox – is more reactive than p-ClPhO – in all solvent mixtures studied (i.e., the α-effect). The α-effect increases as the DMSO content in the medium increases up to 40 mol% DMSO and then decreases beyond that point resulting in a bell-shaped α-effect profile. The bell-shaped α-effect profile obtained for the current reaction is similar to that found previously for the corresponding reaction of p-nitrophenyl acetate (PNPA), differing notably however, in the magnitude of the α-effect beyond 40 mol% DMSO. The PNPB/p-ClPhO – reaction gains greater rate enhancement than the PNPA/p-ClPhO – reaction in the DMSO-rich region, resulting in the smaller α-effect for PNPB beyond 40 mol% DMSO. It is proposed that the observed modulation of the α-effect by the solvent medium is explicable as a ground-state effect in the H 2 O-rich region and a transition-state effect in the DMSO-rich region.Key words: medium effect, the α-effect, ground state, transition state, solvation, desolvation.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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 it