Competing fragmentation processes of <i>O</i> -acetyl-substituted carboxylate anions subjected to collision-induced dissociation
Bibliographic record
Abstract
Carboxylic acids containing an O -acetyl substituent were studied using tandem mass spectrometry (MS/MS). Decarboxylation was observed for deprotonated O -acetylmandelic acid, whereas deprotonated acetoxyacetic acid and acetylsalicylic acid fragmented by two competing pathways. In the lower energy process, the product ion was formed by intramolecular proton abstraction and subsequent neutral loss of ketene (CH 2 =C=O) from the O -acetyl group. At higher collision energies, nucleophilic displacement of the O -acetyl group by the carboxylate group of acetoxyacetate yielded acetate (CH 3 CO 2 – ) as the more abundant product ion. The relative energetics computed for the reaction pathways of acetoxyacetate were consistent with the product ion spectra. Overall, the observation of both the loss of ketene and the formation of acetate ion are characteristic of an O -acetyl group in the precursor carboxylate ion undergoing collision-induced dissociation. The different fragmentation behavior exhibited by O -acetyl mandelate was attributed to the charge stabilizing properties of the phenyl substituent that facilitated decarboxylation. Thus, the fragmentation processes observed depended on the structures of the O -acetyl-substituted carboxylate ions and the associated intramolecular interactions.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.003 |
| 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) | 0.000 | 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 teacher head, 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".