The Decarbonylation of the Acetamide Radical Cation and the Enolization of its Dimer by Self-Catalysis
Bibliographic record
Abstract
The acetamide radical cation, CH 3 C(=O)NH 2 •+ , and its enol, CH 2 =C(OH)NH 2 •+ , undergo several unimolecular reactions in the μs time-frame of which decarbonylation is predominant. This reaction produces the ylid ion CH 2 NH 3 •+ , rather than CH 3 NH 3 •+ [ J. Am. Chem. Soc. 109, 4819 (1987)]. A previously proposed mechanism via ion–dipole complexes is confirmed by the present CBS-QB3 calculations. These calculations reveal the existence of a second mechanism which proceeds via the enol ion and the distonic ion • CH 2 C(=O)NH 3 + . Both mechanisms can account for previously reported isotopic labeling experiments. Tandem mass spectrometry based experiments do not provide evidence that the non-decomposing acetamide ions rearrange to any significant extent to the more stable enol form. However, this transformation occurs smoothly by interaction with a neutral acetamide molecule (“self-catalysis”). By integration of experimental data (MS/MS/MS and labeling experiments) and ab initio calculations [CBS-Q (RHF/DZP)] three mechanisms for this assisted tautomerization have been traced. In the first mechanism the neutral acetamide component of the dimer ion accepts a C–H proton from its ionic partner and then donates the proton back to the oxygen atom. This is an example of “proton-transport catalysis”. In the second mechanism, isomerization takes place within the ionic partner via a conventional 1,3-H shift. The neutral partner serves only to lower the energy of the transition state by ion–dipole attractions. This is an example of the “Spectator” mechanism. In the third mechanism, proton transfer from the ionic partner to its neutral counterpart is followed by back-donation of a hydrogen atom. This is an example of the “Quid-pro-Quo” mechanism. The behavior of the acetamide dimer ion is compared to that of the acetone dimer ion which undergoes only proton-transport catalysis.
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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 | 0.001 | 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".