A photoelectron spectroscopic investigation of aspirin, paracetamol and ibuprofen in the gas phase
Bibliographic record
Abstract
We have investigated the electronic structure of isolated molecules of paracetamol, aspirin and ibuprofen using computational methods and benchmarked the results against valence and core photoelectron spectra. Paracetamol, aspirin and ibuprofen exist as multiple conformers, and we have calculated the free energies and populations of the lowest energy conformers. We find generally good agreement with previous experimental and theoretical structural results. The valence band spectrum of gas phase aspirin has not been reported previously, and we report it and assign the features based on calculations. The effect of acetylation on the frontier orbitals of the parent molecule, salicylic acid, is to increase the ionization potential of the highest occupied molecular orbital (HOMO), and to exchange the energetic ordering of the following two orbitals. The acetyl π bond contributes to the next orbital, which is hybridised with ring π orbitals. The core level spectra of all three molecules are reported and compared with calculations and with the spectra of parent molecules (salicylic acid for aspirin, 4-aminophenol for paracetamol). Observed core ionization energies are in agreement with theory. Although all compounds share a benzene ring, and they also have a number of other chromophores in common, the spectroscopic data indicate chemical diversity, suggesting that their modes of bonding under physiological conditions are likely to be diverse.
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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 | 0.000 | 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 | 0.001 |
| 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".