Generation, observation, and reactivity of furyl- and thienylketenes and bisketenes
Bibliographic record
Abstract
2- and 3-Furylketenes (18 and 20), 2- and 3-thienylketenes (19 and 21), and bis(2,5-ketenyl)thiophene (24) have been generated as observable reactive intermediates by photochemical Wolff rearrangements. Stabilization energies of the monoketenes 18–21 have been determined by DFT computations of isodesmic energy changes, and these ketenes are predicted to be modestly destabilized relative to phenylketene. Rate constants for reaction of 18–21 with H2O and with n-BuNH2 have been measured and are similar to those of the 2-, 3-, and 4-pyridylketenes (1). The product of reaction of 2-furylketene (18) with H2O is calculated to be stable as an acid enol, and reaction of 18 with the stable free radical TEMPO forms a stable ester enol, consistent with stabilization by intramolecular H-bonding to the furyl oxygen. Bis(thienyl)-1,2-bisketenes 26 and 28 have been generated by photochemical cyclobutenedione ring opening and are highly reactive in ring closure. This is attributed to destabilization of the ketenes and stabilization of the cyclobutenediones by the electron donating aryl groups.Key words: ketenes, furans, thiophenes, reactive intermediates, photolysis, mechanisms.
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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) | 0.001 | 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".