Thermodynamic functions of conformational changes I. A comparative first principles study of 1,2-disubstituted ethanes
Bibliographic record
Abstract
The conformational changes of ethane and disubstituted ethanes, X–CH2–CH2–X, where X were hydrogen isotopes of higher masses, −F atoms and −CH3 groups, were investigated by CBS-4M and MP2/6-311G(d,p) computational levels. Thermodynamic functions such as ΔH, ΔG and S were computed along the approximate reaction coordinate of conformational changes. The lowest frequency associated with the rotation about the central C–C bond was omitted along the whole reaction path. The thermodynamic functions were continuous in the case when only 3N–7 internal degrees of freedom were taken into consideration. Identical results were obtained using projected frequency calculations in the surroundings of rotational transition states. The effect of the mass and electronic difference on the entropy of the two key compounds (X = F and X = CH3) were separated and assessed. The periodicity of reaction coordinates determined the periodicity of the thermodynamic functions. The second derivatives of the potential energy functions had a shape similar to the entropy functions. The enthalpy was plotted as a function of entropy and rotational reaction coordinate. The concept of ‘entropy funnel’ used by protein chemists was recognized even in the cases of the simple compounds investigated. We concluded that the bottom of the entropy funnel could correspond to the gauche conformers, in accordance with the concept of protein folding.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 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 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".