Rotational spectroscopy of chiral tetrahydro-2-furoic acid: Conformational landscape, conversion, and abundances
Bibliographic record
Abstract
The conformational landscape of tetrahydro-2-furoic acid (THFA), a chiral carboxylic acid which is often used as a precursor in syntheses of pharmaceuticals, was investigated using rotational spectroscopy and theoretical modeling. Extensive manual searches were carried out to identify possible conformers related to the relative orientations of the carbonyl and hydroxyl groups in the COOH functional group, the COOH rotation, and the ring puckering motions in the system. A large number of initial conformational geometries were generated in parallel using a joint semiempirical-molecular dynamics simulation program. The final geometry optimizations were carried out at the B3LYP-D3(BJ)/def2-TZVP, B3LYP-D3(BJ)/6-311++G(2d,p), and MP2/6-311G++(2d,p) levels of theory. Eight conformers within a relative energy span of 10 kJ mol−1 after zero-point energy corrections were identified. Rotational spectra of three conformers were detected experimentally and assigned, as were the spectra of all the 13C isotopologues of the most stable conformer. Based on the achieved experimental sensitivity and the predicted relative abundances at the sample source, some conformers are unexpectedly missing or experience significant depletion, whereas others show noticeable enrichment. Detailed analyses of the conformational conversion barriers were carried out to satisfactorily explain the observed phenomena. The combined experimental rotational spectroscopic and theoretical investigation provides significant insights into the complex conformational landscape of THFA.
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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 | 0.000 |
| 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".