Intramolecular and Intermolecular Hydrogen Bond Formation by Some Ortho-Substituted Phenols: Some Surprising Results from an Experimental and Theoretical Investigation
Bibliographic record
Abstract
The effects produced by addition of various concentrations of the strong hydrogen bond (HB) acceptor, dimethyl sulfoxide (DMSO), on the OH fundamental stretching region of the IR spectra of several o-methoxy, o-nitro, and o-carbonyl phenols in CCl(4) are reported. In most of these phenols the intramolecular HB is not broken by the DMSO. Instead, the DMSO acts as a HB acceptor to the intramolecular HB forming a bifurcated intra/intermolecular HB. For o-methoxyphenols the bifurcated HBs are observed as new IR bands at much lower wavenumbers (Deltanu(OH) approximately -300 cm(-1)) than the band due to their intramolecular HB. The formation of bifurcated HBs and the large frequency shift of their OH bands in o-methoxyphenols are well reproduced by theoretical modeling. In contrast to the o-methoxyphenols DMSO has little effect (other than causing some broadening) on the intramolecular HB OH bands of o-nitro and o-carbonyl phenols, with the single exception of 2,4-dinitrophenol. In this case, but not for 2,4-diformylphenol, the intramolecular HB OH band decreases as the DMSO concentration increases and a new absorption grows in at lower wavenumbers, indicating that DMSO can break this intra-HB and form an inter-HB, a result well reproduced by theory. Although DMSO has little effect on the O-H stretching band of 2-nitrophenol, theory indicates extensive formation (90%) of bifurcated HBs with OH stretching bands at slightly higher wavenumbers (Deltanu(OH) approximately +20 cm(-1)) than that for the intramolecular HB OH group and 10% of a "simple" intermolecular HB in which the intramolecular HB has been broken. Theory also indicates that, with DMSO, 2-formylphenol also forms a bifurcated HB (Deltanu(OH) approximately +150 cm(-1)), whereas 2,4-diformylphenol forms both intermolecular HBs (Deltanu(OH) approximately -130 cm(-1)) and bifurcated HBs (Deltanu(OH) approximately +165 cm(-1)). The IR spectrum of 2-methoxymethylphenol shows that although an intramolecular HB conformer is dominant there is a small percentage of a "free" OH, non-HB conformer (2.1% in CCl(4), 1.5% in cyclohexane). These results are quantitatively reproduced by theory. We conclude that theory can provide important insights into the formation and structure of inter, intra, and bifurcated HBs, and into their OH stretching frequencies, that are not always revealed by IR studies alone.
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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 | 0.001 |
| 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".