The Fate of Protonated Guaiacol and Its Derivatives in the Gas Phase
Bibliographic record
Abstract
Guaiacol (2-methoxyphenol) and its derivatives are a class of semivolatile polar organic molecules possessing low molecular weights. Owing to their volatility, guaiacol and its derivatives can interact with atmospheric water and form protonated methoxyphenols through proton transfer. The aim of the present work is to study the dissociation of these protonated ions and hence, potentially, their atmospheric fate. Tandem mass spectrometry was employed to analyze the unimolecular dissociation of the protonated forms of guaiacol (2-methoxyphenol, 1 ), creosol (2-methoxy-4-methylphenol, 2 ), 4-ethylguaiacol (4-ethyl-2-methoxyphenol, 3 ), 4-vinylguaiacol (2-methoxy-4-vinylphenol, 4 ), eugenol (2-methoxy-4-prop-2-enylphenol, 5 ), and vanillin (4-hydroxy-3-methoxybenzaldehyde, 6 ). Density functional theory at the B3LYP/6-31G(d) ( 1 – 5 ) and B3LYP/6-311+G(d,p) ( 6 ) levels of theory were applied to determine the observed minimum energy reaction pathways, and reliable energetics were acquired using CBS-QB3 single-point energy calculations. All the protonated ions, with the exception of 6, exhibit the loss of CH 3 OH via a series of hydrogen transfers, followed by ring contraction to lose CO. This common dissociation pathway leads to the formation of a cyclopentadienyl ion as the main dissociation product. Conversely, 6 first exhibits the loss of CO, followed by sequential losses of CH 3 OH and CO to generate a cyclopentadienyl ion. Additionally, minor fragmentation channels are also observed for the different protonated ions: CH 2 loss in 1; CH 4 and H 2 O losses in 3; CH 3 loss in 4, 5, and 6; C 2 H 4 and CH 2 CHCH 2 losses in 5; H loss in 6 . Altogether, the protonated ions primarily lose CH 3 OH and CO as neutral molecules and generate a cyclopentadienyl ion as a dissociation product.
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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 | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".