A theoretical and experimental investigation of some unusual intermolecular hydrogen-bond IR bands — Appearances can be deceptive
Bibliographic record
Abstract
The IR spectra of the O-H stretch for hydrogen bonds (HBs) arising from complex formation between the HB donor (HBD), 4-fluorophenol, and the HB acceptors, peroxides and ethers, frequently show asymmetry that appears to arise from two incompletely resolved bands from two different complexes, but the O-H HB bands with the HBD methanol are symmetric (M. Berthelot, F. Bessau, and C. Laurence. Eur. J. Org. Chem. 925 (1998)). The present studies show that this difference in O-H HB band shapes also is true for other phenols and alcohols. However with ethylene oxide, 4-fluorophenol gives an almost symmetric O-H HB band with a very broad maximum, while alcohols give symmetric O-H HB bands with well-defined maxima. It is shown by experiment that the unusual O-H HB band shapes for the phenols are not due to Fermi resonance and are unrelated to the enthalpies of HB complex formation. Theoretical exploration of the potential energy (PE) surfaces for complexes of 4-fluorophenol and methanol with tert-butyl methyl ether and ethylene oxide reveals that O-H HB band asymmetry or broadness cannot be ascribed to the presence of two different HB complexes. For this ether, the PE surfaces for rotation about the HB and for up-and-down motion of the HBD with respect to the COC plane of the ether are relatively symmetric for methanol, but are strongly asymmetric for 4-fluorophenol, hence the differences in the O-H HB band shapes. The PE surfaces for the epoxide are effectively symmetric, but the PE for rotation about the HB has a single broad minimum for methanol, whereas with 4-fluorophenol there are two minima owing to attractive interactions between the phenyl group and the CH 2 groups of the epoxide. The previously unknown β 2 H values for ethylene oxide and tetramethylethylene oxide are 0.36 and 0.58, respectively.Key words: asymmetric IR O-H bands, asymmetric potential energy surfaces, hydrogen-bonded complexes, hydrogen bond enthalpy, O-H frequency shift.
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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 | 0.001 |
| 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 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".