Benzooxirene, naphthooxirenes, and anthraceneoxirenes: the stabilization of the oxirene system by bond fixation in acenes. A comparison of ab initio and DFT in the investigation of annelated oxirenes
Bibliographic record
Abstract
The effect on the stabilities of benzoannelated oxirenes (oxacyclopropenes) of variations in the C-C bond electron density (as measured by Löwdin bond order) was studied computationally. Benzo[b]oxirene (4ox), naphtho[2,3-b]oxirene (5ox), naphtho[1,2-b]oxirene (6ox), anthro[2,3-b]oxirene (7ox), and anthro[1,2-b]oxirene (8ox) were investigated using the DFT pBP/DN* method as implemented in the program Spartan. This method was chosen because with 4ox it gave results similar to those from the much slower QCISD(T)/6-31G*//MP2(full)/6-31G* and MP4SDTQ/6-31G*//MP2(full)/6-31G* methods. The calculated barriers to oxirene ring opening for the "linear" 4ox, 5ox, and 7ox (bond orders 1.35, 1.24, and 1.20, respectively) were 23.6, 39.9, and 46.6 kJ mol-1, in contrast to the "angular" 6ox and 8ox (bond orders 1.50 and 1.59, respectively), with barriers of ca. 0 kJ mol-1. The high-barrier vs. low-barrier series corresponds to the stabilities expected from the resonance structures of the oxirenes or their formal precursor acenes. Empirically, the ring-opening barriers were linearly related to the oxirene bond orders, and extrapolation to tetracene using this relationship gave a barrier of ca. 50 kJ mol-1, which seems to be the limiting barrier in the linear series. In several cases the oxirene isomerized to a ketene without going through an oxo carbene (ketocarbene). Benzoannelation is only the second kind of substitution (after dimethyl substitution) that has been indicated, computationally, to be able to stabilize oxirenes.Key words: oxirenes, ketocarbenes, benzooxirenes, AM1, ab initio, DFT.
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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) | 0.004 | 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".