Effect of medium on reactivity for alkaline hydrolysis of <i>p</i>-nitrophenyl acetate and <i>S</i>-<i>p</i>-nitrophenyl thioacetate in DMSO–H<sub>2</sub>O mixtures of varying compositions: ground state and transition state contributions
Bibliographic record
Abstract
Second-order rate constants (k N ) for reactions of p-nitrophenyl acetate (1) and S-p-nitrophenyl thioacetate (2) with OH – have been measured spectrophotometrically in DMSO–H 2 O mixtures of varying compositions at 25.0 ± 0.1 °C. The k N value increases from 11.6 to 32 800 M –1 s –1 for the reactions of 1 and from 5.90 to 190 000 M –1 s –1 for those of 2 as the reaction medium changes from H 2 O to 80 mol % DMSO, indicating that the effect of medium on reactivity is more remarkable for the reactions of 2 than for those of 1. Although 2 possesses a better leaving group than 1, the former is less reactive than the latter by a factor of 2 in H 2 O. This implies that expulsion of the leaving group is not advanced in the rate-determining transition state, i.e., the reactions of 1 and 2 with OH – proceed through a stepwise mechanism, in which expulsion of the leaving group from the addition intermediate occurs after the rate-determining step. Addition of DMSO to H 2 O would destabilize OH – through electronic repulsion between the anion and the negative-dipole end in DMSO. However, destabilization of OH – in the ground state is not solely responsible for the remarkably enhanced reactivity upon addition of DMSO to the medium. The effect of medium on reactivity has been dissected into the ground state and transition state contributions through combination of the kinetic data with the transfer enthalpies (ΔΔH tr ) from H 2 O to DMSO–H 2 O mixtures for OH – ion.
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How this classification was reachedexpand
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 | 0.001 | 0.001 |
| 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".