Electron Transfer Properties of Alkoxyl Radicals. A Time-Resolved Kinetic Study of the Reactions of the<i>tert</i>-Butoxyl, Cumyloxyl, and Benzyloxyl Radicals with Alkyl Ferrocenes
Bibliographic record
Abstract
A time-resolved kinetic study on the reactions of the tert-butoxyl (t-BuO*), cumyloxyl (CumO*), and benzyloxyl (BnO*) radicals with alkylferrocenes has been carried out in MeCN solution. With all radicals, clear evidence for an electron transfer (ET) process has been obtained, and with the same ferrocene donor, the reactivity has been observed to increase in the order t-BuO* < CumO* < BnO*, with the difference in reactivity approaching 3 orders of magnitude on going from t-BuO* to BnO*. With BnO*, an excellent fit to the Marcus equation has been obtained, from which a value of the reduction potential of BnO* (E degrees(BnO*/BnO(-)) = 0.54 V/SCE) has been derived. The latter value appears, however, to be significantly higher than the previously determined reduction potential values for alkoxyl radicals and in contrast with the differences in the computed solution-phase electron affinities determined for t-BuO*, CumO*, and BnO*, indicating that the reaction of BnO* with ferrocene donors may not be described in terms of a straightforward outer sphere ET mechanism. From these data, and taking into account the available value of the reduction potential for CumO*, a value of E degrees (BnO*/BnO(-)) = -0.10 V/SCE has been estimated. On the basis of computational evidence for the formation of a pi-stacked prereaction complex in the reaction between BnO* and DcMFc, an alternative ET mechanism is proposed for the reactions of both CumO* and BnO*. In these cases, the delocalized nature of the unpaired electron allows for the aromatic ring to act as an electron relay by mediating the ET from the ferrocene donor to the formal oxygen radical center. This hypothesis is also in line with the observation that both BnO* and CumO* react with the ferrocene donors with rate constants that are in all cases at least 2 orders of magnitude higher than those measured for t-BuO*, wherein the radical is well-localized.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 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".