Substituent effects, Arrhenius activation parameters, and rate constants for the photo–Claisen rearrangement of allyl aryl ethers
Bibliographic record
Abstract
The temperature-dependence of fluorescence quantum yields in both methanol and methylcyclohexane has been used to obtain the rate constants of reaction for the activated process that converts the singlet excited state S1 of a set of ring-substituted aryl allyl ethers to an intermediate radical pair in the photo–Claisen rearrangement. These rate constants are correlated with the O–H bond dissociation energy of the corresponding ring-substituted phenols; that is, electron-donating groups (CH3, OCH3) accelerate the reaction relative to electron-withdrawing groups (CF3, CN). The rate constants obtained span two orders of magnitude, from 5.4 × 107 s–1 for X = 3–CN to 800 × 107 s–1 for X = 4–OCH3, in methylcylcohexane. Moreover, the rate constants are similar in the two solvents, methanol and methcyclohexane, indicating that radical pairs, not ion pairs, are the reactive intermediates, as expected on the basis of previous mechanistic proposals for the photo–Claisen rearrangement. Finally, the rate constants obtained by this temperature-dependent method are in good agreement with those previously reported from a method using the corresponding unreactive anisoles as a model.Key words: allyl aryl ethers, photo–Claisen rearrangement, substituent effects, activation parameters.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".