Mechanism of the Major Orientation Polarization in Alcohols, and the Effects of Steric Hindrance-, and Dilution-Induced Decrease on H-Bonding
Bibliographic record
Abstract
To gain insight into the effects of intermolecular H-bond association on the changes in permittivity and relaxation characteristics of supercooled alcohols, two techniques were used here: (i) introducing a C 6 H 5 group in 2-propanol to obtain 1-phenyl-2-propanol, and thus increasing the steric hindrance to H-bonding, and (ii) dissolving the latter in 2-methylpentane and thus decreasing the extent of H-bonding by separating molecules in a nonpolar solvent. Broad-band dielectric spectroscopy studies of supercooled liquid 1-phenyl-2-propanol and its 1:1 (mol:mol) mixture in 2-methylpentane were performed over the 188−238 K range. These show that ∼94% of the total polarization decays according to the Davidson−Cole distribution of relaxation times and that the equilibrium permittivity decreases when phenyl group is substituted in 2-propanol. Analysis in terms of the statistical theories of dielectric behavior shows that the decrease is due to a decrease in the orientation correlation factor, and that this also occurs in the mixture with 2-methylpentane. The induced steric hindrance reduces the extent of intermolecular H-bonding in comparison with that of 2-propanol. The relaxation rate follows the non-Arrhenius temperature dependence. It has been examined qualitatively in terms of the Dyre theory which considers that the apparent Arrhenius energy itself is temperature-dependent, as in the classical interpretations, and quantitatively in terms of the cooperatively rearranging region's size, without implying that there is an underlying thermodynamic transition in its equilibrium liquid. The relaxation rate also fits the power law with the critical exponent of 14.52 for 1-phenyl-2-propanol and 12.9 for the mixture, instead of 2 to 4, usually required by the mode-coupling theory. This indicates the ambiguity of the power-law equations. The excess dielectric loss observed at high frequencies may indicate Nagle's “wing”, or else a merged Johari−Goldstein relaxation.
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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 | 0.000 | 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 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".