Insight into Methyl <i>tert</i>-Butyl Ether (MTBE) Stable Isotope Fractionation from Abiotic Reference Experiments
Bibliographic record
Abstract
Methyl group oxidation, SN2-type hydrolysis, and SN1-type hydrolysis are suggested as natural transformation mechanisms of MTBE. This study reports for the first time MTBE isotopic fractionation during acid hydrolysis and for oxidation by permanganate. In acid hydrolysis, MTBE isotopic enrichment factors were epsilon(C) = -4.9 per thousand +/- 0.6 per thousand for carbon and epsilon(H) = -55 per thousand +/- 7 per thousand for hydrogen. Position-specific values were epsilon(C), reactive position = -24.3 per thousand +/- 2.3 oer thousand and epsilon(H,reactive position) = -73 per thousand +/- 9 per thousand, giving kinetic isotope effects KIE(C) = 1.025 +/- 0.003 and KIE(H) = 1.08 +/- 0.01 consistent with an SN1-type hydrolysis involving the tert-butyl group. The characteristic slope of deltadelta2H(bulk)/deltadelta13C(bulk) approximately epsilon(bulk,H)/ epsilon(bulk,C) = 11.1 +/- 1.3 suggests it may identify SN1-type hydrolysis also in settings where the pathway is not well constrained. Oxidation by permanganate was found to involve specifically the methyl group of MTBE, similar to aerobic biodegradation. Large hydrogen enrichment factors of epsilon(H) = -109 per thousand +/- 9 per thousand and epsilon(H,reactive position) = -342 per thousand +/- 16 per thousand indicate both large primary and large secondary hydrogen isotope effects. Significantly smaller values reported previously for aerobic biodegradation suggest that intrinsic fractionation is often masked by additional non-fractionating steps. For conservative estimates of biodegradation at field sites, the largest epsilon values reported should, therefore, be used.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.011 | 0.003 |
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; both teacher heads agree on what is shown here.
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".