Fragmentation pathways arising from protonation at different sites in aminoalkyl‐substituted 3‐hydroxy‐1,2,5‐oxadiazoles (3‐hydroxyfurazans)
Bibliographic record
Abstract
Rationale The gas‐phase fragmentation chemistry of multifunctional cations is highly influenced by the site of protonation. Possible relationships between protonation site and fragmentation processes were studied using 4‐aminoalkyl‐3‐hydroxyfurazans. For these heterocyclic amines, the starting points for competing fragmentation pathways varied with protonation at multiple sites in two tautomers. Methods Mass spectra were acquired using electrospray ionization (positive mode) coupled to triple quadrupole and ion trap mass spectrometers; precursor–product ion relationships were studied by collision‐induced dissociation. Quantum mechanical computations were performed at the MP2/6–311++G(2d,p)//ωB97X‐D/6–311+G(d) level of theory. Results Prominent successive losses of NO and CO and competing losses of CH 2 =NH or NH 3 were observed as fragmentation processes. The lowest barrier computed for the initial step in a fragmentation pathway was associated with the [M + H] + ion protonated at N5 in the heterocyclic ring, whereas an alternative ring cleavage leading to complementary product ions was initiated by protonation of the ring at N2. Side‐chain protonation led to loss of NH 3 without cleavage of the 3‐hydroxyfurazan ring. Conclusions The product ions obtained by the competing fragmentation processes varied with the site of protonation. Interestingly, the most abundant product ions observed at low collision energies were formed by cleavage of protonated molecules possessing more internal energy than other isomers.
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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".