Density Functional Theory Based Model Calculations for Accurate Bond Dissociation Enthalpies. 2. Studies of X−X and X−Y (X, Y = C, N, O, S, Halogen) Bonds
Bibliographic record
Abstract
The bond dissociation enthalpies for a set of 30 compounds containing X−Y (X, Y = C, N, O, S, halogen) bonds are computed using density functional theory based model approaches with the B3P86 functional. These types of bonds were chosen because of their particular importance in free radical organic and bio-organic chemistry, specifically redox chemistry and atom transfer reactions. A series of test calculations on hydrogen peroxide, propane, and methyl chloride led to the choice of the 6-311G(d,p) basis set for optimum performance in terms of speed and accuracy. Three models are defined and tested. The lowest level model, which is capable of treating systems containing more than 30 non-hydrogen atoms, predicts bond dissociation enthalpies with a mean absolute deviation of 2.38 kcal/mol relative to experiment. For a subset of 21 molecules, the two higher-level models predict results with mean absolute deviations of 1.88 and 2.19 kcal/mol relative to experiment. Test calculations on X−H bond energetics indicate that two separate approaches are required for the accurate treatment of both X−Y and X−H bonds.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.001 |
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".